Bluff the Impostor

"The Terminator: (to John) What's the dog's name? John Connor: Max. The Terminator: (impersonating John's voice) Hey Janelle, what's wrong with Wolfie? I can hear him barking. Janelle : He's fine, John. Wolfie's just fine. Where are you? The Terminator: (hangs up) Your foster parents are dead."

- Terminator 2: Judgment Day

Your best friend/loved one/respected figure of authority is acting strangely and you suspect—with good reason—that he or she may in fact be an impostor. So what do you do? Assuming that the impostor didn't research his role perfectly, you Bluff the Impostor: ask a question, make a comment, say something that sounds natural to the potential impostor... but mine it with an erroneous fact or two, like a wrong name or a fictional event, and see if they repeat the mistake, or try to bluff.

Related to You Just Told Me and Spot the Imposter. May involve Spy Speak. See also Cover Identity Anomaly and Something Only They Would Say, for when the impostor says something that breaks his or her cover, intentionally or not. Contrast I Never Said It Was Poison and Trust Password. May involve Exasperated Perp.

Anime and Manga
""What are you doing, Lieutenant? Don't you know who your gun's pointed at?" "Who? Don't make me laugh. When we're alone the Colonel always calls me by my first name, Riza." "Grk!" *dives away, transforming back into Envy* "So you two are that close, are you?" "I Lied." *BANG* "But thanks for falling for it. Now you can do me the favor of dying.""
 * In Yami no Matsuei, Hisoka suspects that Tsuzuki is possessed by a demon and tells him, as usual, to bring something to eat for the Chief. He "reminds" Tsuzuki that the Chief hates sweets, and when Tsuzuki falls for it, he knows it's an impostor.
 * In From Eroica with Love, Major Eberbach tests if a guide who called him is a KGB spy by asking her about a fictitious aunt. When the guide gets confused, he concludes she's no spy, because a spy would've pretended to know the woman.
 * Naruto
 * Sasuke came up with a very long and convoluted "password" for his two teammates to memorize in case they ever needed confirmation of one another's identity. Naruto leaves to go to the bathroom, and when he comes back, Sasuke asks him to code in. Naruto repeats it back perfectly... and Sasuke decks the imposter, declaring that the real Naruto would never have been able to remember something that long.
 * Later, the Mizukage does this quite expertly.
 * Naturally, Naruto is too stupid to pull one of these himself. In one filler arc, he, Hinata and Kiba have to deal with impostors copying their every facet. So naturally when trying to identify the real Hinata, rather than asking a baited question like, "Hey, Hinata, how did you defeat Neji during the Chuunin exams?" he inverts the trope, asking, "What is the name of Hinata's father?"- a question any good imposter would study beforehand, but one that Naruto himself didn't know the answer to, making it utterly useless even if the imposter didn't know!
 * Sakura pulls one of these off
 * Episode 333: The imposter shows up in front of the real Naruto Uzumaki and declares that he is Naruto Uzumaki. Until Naruto said that he was the real one and the imposter got curbstomped.
 * Used in the Fullmetal Alchemist manga: Riza Hawkeye and Roy Mustang are hunting down the shapeshifting Envy and get separated; when they meet up again, they exchange a few words, then start off looking for Envy... until Hawkeye puts her gun to Mustang's head. This leads to a universal "oh crap" from the fanbase, until…


 * Done heartbreakingly in Karin (with a bottle of Tabasco sauce) towards the end of the manga, to determine if the titular character's sister has matured to the point where scheduling differences now leave her without any daywalking family. Adult vampires, you see, have no sense of taste.
 * In Guyver, protagonist Sho is handcuffed to love interest Mizuki so he can't bio-boost without blasting the broad to bloody bits. Hearing half a warning that she might not be who she appears to be, Sho laments that this had to happen right after Mizuki's birthday. She agrees, and her cover is blown because Sho knows her birthday is later in the year.
 * Love of Fresh Pretty Cure! bluffs an impostor of her mother by switching her and Setsuna's presents and thanking her for the wrong one. Since Love is an Idiot Hero, everybody else had already figured out that the Ayumi living with them was a fake already, but it's the thought that counts.
 * In Digimon Xros Wars, episode 39, Kiriha suddenly remembers to return a Digimemory he borrowed from Taiki, and Taiki agrees. Except that the borrowing never happened, and Kiriha hands over a small explosive device that ruins Splashmon's impersonation of Taiki.
 * In Love Hina, Keitaro lies about being a student at Tokyo U, so Naru asks him about the miso-boiled lobster they serve in the cafeteria. Keitaro babbles on for a bit about how it's his favourite food that he can't start the day without, before Naru tells him that there is no such thing as a miso-boiled lobster.

Comic Books

 * In the Team 7/Weapon X crossover, the two squads meet in an underground base they were both tasked with blowing up. At gunpoint, they ask each other sports questions to find out if they are Soviets. Amusingly, Wolverine (a Canadian) asks a hockey question, which would probably be more easily answered by a Russian than an American.
 * In Doctor Strange: The Oath, Doctor Strange encounters a demonic entity who tries to convince Strange that he is facing one of his most powerful foes, Dormammu. Strange, suspicious of Dormammu's sudden arrival, asks him, "So where is Umar, your rapscallion of a brother?" When Dormammu answers, "He is none of your concern," Strange has his answer; Umar is Dormammu's sister.

Films -- Live-Action
"Ellen: Reminds me of when you were in the state legislature. Dave: Yeah... me too. Ellen: You weren't in the state legislature. (stands up and offers her hand) Hi, I'm Ellen Mitchell. Who are you?"
 * In Terminator 2: Judgment Day, the T-800 asks John Connor's foster mother a question about the family dog but intentionally gives the wrong name to see if she's actually the shapeshifting T-1000.  There is a deleted scene where the T-1000 is shown afterwards holding a bloody dog collar, seeing the name on it and realizing that his target knows that he is there and will be avoiding the house.
 * In Live Free or Die Hard John McClane mentions a police code to the Big Bad's girlfriend, who is disguised as a police dispatcher. She says that the police had to dispatch all units in regards to the code. McClane coolly responds, "Dispatch all units for the naked people running around?"
 * In Darkman, the villain comments to the title hero, while the hero is in disguise, that he would hate for his (the person who Darkman is impersonating) wife and kids to miss out on such a "great role model." When Darkman answers that they do look up to him, the villain casually notes that he doesn't have any kids, and nailguns his hand to the wall.
 * Darkman 2: Durant (the villain) suspects that Darkman is masquerading as Ivan, and to make sure he makes a comment about not having to leave someone's body behind in Saskatoon. He was refering to an earlier conversation, where he's talking to the woman in question in Ivan's presence and states that they'll be burying her in Saskatchewan.
 * From Dave:

"Devlin: Oh, by the way, your wife called. disguise!Pistachio: Oh. Thanks. Devlin: You're welcome. (Turns away, then turns back) YOU'RE NOT MARRIED! (rips off Pistachio's disguise)"
 * The main villain of The Master of Disguise uses this in one of the final scenes to uncover the identity of the disguised hero, who had given himself away by forgetting to change his shoes.

"Clouseau: What is your code name? Dreyfus: I don't have a code name! I never had a code name, lunatic! Clouseau: I understand sir, but you see, only the real Inspector Dreyfus would know he did not have a code name."
 * In the Spiderwick Chronicles movie, the main character's father seems to appear and he (the kid) asks his dad what it was he wanted to tell him.
 * Used in The Return of the PinkPanther:

"Lady: Did you see the ad in the Times? Patrick: Uh, yeah. Lady: There was no ad in the Times."
 * In American Psycho:

"T.K.: That first time we met at the bookstore, did you ever imagine we'd end up in a mess like this? Yulaw: Even if I had known, I still would have done it. T.K.: (turns gun on Yulaw) It wasn't a bookstore."
 * In The One, when Gabe's Evil Twin tries to take his place:


 * In Invasion U.S.A. (not the Chuck Norris one, the Cold War one), several Soviet paratroopers approach Washington D.C. disguised in U.S. Army uniforms, in the latest phase of the titular invasion. They're stopped by a guard who notices that the troops are "apparently" from Chicago. The guard asks the leader of the troops if he ever saw the Cubs play. The confused leader says, "Cubs? A cub is a small animal, a bear."
 * In The Negotiator, Sabian is trying to talk down negotiator-turned-hostage-taker Danny Roman. When Roman demands to talk to a confidential informant that can't be located, Sabian reasons that Roman doesn't know the guy either. He substitutes an impostor but is caught when Roman slips in a reference to the impostor's time playing ball for Colorado State and the impostor fails to challenge it despite having Arizona State in his personnel file.
 * Eyes Wide Shut: This is how Bill is called out during the orgy sequence. He's asked for the house password in addition to the admittance password, which he says he forgot. Later on, he's told that there was no house password.
 * In Ronin,
 * In Alone with Her, when the protagonist, the girl he's secretly spying on/manipulating, and her best friend are having lunch, the best friend asks him if he'd been to a particular fashion district in Seattle (since he claims to be from Seattle). He says yes, and once he's out of the room, the best friend reveals that she made the fashion district up.
 * The Jet Li film Black Mask has one of the villains claim to be leading Li's best friend, a cop, to where Li is hiding, posing as a new transfer from the friend's old district. He's asked about a Captain Chan, and says he knows him and he's a nice guy. Then he's immediately shot: "Chan died four years ago, and he was a real prick!"
 * In There Will Be Blood, Plainview recalls events in his hometown to test whether his half-brother really is who he says he is.
 * Stalag 17: The Mole tips off suspicious cabinmates by mentioning that he was eating dinner when the attack on Pearl Harbor occurred. While it was noon in the Eastern time zone when the attack happened, it was dinnertime in Germany.
 * Variation in Men in Black: Agent K exposes an alien posting as a Mexican immigrant by saying insulting and threatening things in Spanish, but in a cheery tone of voice, to see if he reacted appropriately.
 * In the Gene Hackman film Narrow Margin, Hackman's character tells a pair of "RCMP officers" that he might have the guys who've been pursuing him and his witness all over a train "on a 374". They agree, which tips him off to their being fake. 374 is "indecent exposure".

Gamebooks

 * In the third book of the Lone Wolf series, The Caverns of Kalte, Lone Wolf meets a prisoner in the enemy's fortress, who pretends to be a merchant from Ragadorn, . The game allows asking him a few questions about the city of Ragadorn (visited by Lone Wolf in his earlier quest), . The text never points out whether he is right or not, however: it is up to the player to remember what are the correct answers from the previous book.

Literature

 * Harry Potter
 * In Harry Potter and the Half-Blood Prince, the Ministry advises people to ask this kind of question to make sure a Death Eater isn't impersonating your friend. Harry quickly figures out for himself that when magical compulsion is one of the favorite tools of the bad guys, this sort of thing is the barest of bare-bones contingencies.
 * It's also inverted: Arthur Weasley comes home from the Ministry and passes Molly's challenge at the door. When she goes to open it, he grabs it and pulls the door shut again so he can challenge her. Afterwards, Molly comments that it's silly, since anyone impersonating Arthur could easily torture the question and response out of him. He agrees with her, but says that they should do it to set an example.
 * In Harry Potter and the Deathly Hallows, members of the Order of the Phoenix start doing this to each other. Guess they decided the idea wasn't so useless after all. There is the slight variant that they don't agree on what questions to ask beforehand, instead just asking about random moments in their past, making the system more secure.
 * In Robert A. Heinlein's Double Star, a disguised actor impersonating a politician meets with the Emperor of the Solar System. The Emperor insists that he play with his toy trains, which the actor dutifully does. The Emperor then asks him who he really is, because all the past times he had met with the politician and asked him to play with the trains the politician had refused and teased him about having such a childish hobby—it was a sort of game between them.
 * It was an interesting play on this trope, as the actor's impersonation was so flawless that the Emperor hadn't really been all that suspicious until that point.
 * In The Savage Damsel and the Dwarf, the title characters are staying with a group of knights, and the dwarf mentions that he used to serve Sir Gaheris. One of the knights asks casually if Sir Gaheris is still as skilled a swordsman as ever. The dwarf  passes the test when he responds that the knight must be thinking of someone else, since Sir Gaheris is a notoriously abysmal swordsman.
 * Played with in one of the Animorphs books, when David acquires Marco. Rachel taunts the real Marco with "You know you're a toad, right?" and Cassie asks him to describe how it felt when they morphed trout. They know it's Marco because he answers sarcastically ("Kiss me and I'll become a prince," and "The cracker crumb coating chafed," respectively).
 * Marco does beg for them to not try this, because he's terrified that he'll miss a punchline, and Rachel will eat him before he has a chance to explain. (Although, that could be sarcasm, too...)
 * In another book, a Controller says the word "Andalite!" loudly to a person he suspects to be an "Andalite bandit" in human morph. In reality, he's as close to being right as you can be, as the person in question is Cassie in Rachel morph. But he's satisfied when, without missing a beat, Cassie/Rachel immediately replies as if he had just said the words "and a light".
 * Marco also does this after his dad discovers Z-space, trying to see if his dad's a controller by pointing out that the trip his dad wants to take would mean they'd be gone more than three days, the amount of time a Yeerk can go between feedings.
 * A variant occurs in The Odyssey: Penelope uses this to see whether the man claiming to be Odysseus after 20 years really is her husband. She orders their bed to be moved back to their bedroom; Odysseus protests that this couldn't be done as he carved the bedpost himself out of a living olive tree, thus proving his identity. Making this one Older Than Feudalism.
 * In one of the Ranger's Apprentice books, Will is in disguise as a minstrel. The lord of the castle he's visiting asks if his instrument was made by the master luthier Gilperon, and Will says no. Later the lord informs him that the luthier's name is actually Gilet, which a real musician would have known.
 * In John Barnes's One for the Morning Glory, the Duke challenges Sir John to name Calliope's birthmark on her thigh. Sir John sputters. Given that with Sir John's reputation, any imposter would have improvised because of course Sir John would have known.
 * Used in Dan Abnett's third Eisenhorn book, Hereticus. Eisenhorn spots an imposter posing as a trusted member of his retinue by saying their situation reminded him of the tight spot they'd been in fighting Beldame Sadia on Eechan. The imposter agrees, alerting Eisenhorn (and any particularly astute readers) to the trick—they'd actually fought Sadia on Lethe Eleven.
 * Subverted twice and played straight once in Isaac Asimov's short story "Little Lost Robot". Robots in this universe are normally "Three Laws"-Compliant, but a few special robots have been made with a modified First Law: while they still cannot harm a human being, they have no problem letting human beings be harmed by outside forces. The heroine wants to find one such robot who has hidden himself in a roomful of normal robots. Three attempts are made to invoke this trope. The lost robot foils the first because, while it doesn't have to rescue a human in danger, it can choose to do so. So they try to put the robot in a situation where trying to rescue a human would (as far as it knows) destroy it (prohibited by the Third Law unless trumped by the First or Second). Indeed, the robot does not try to rescue the human—but has cleverly convinced the other robots not to try either (they'd be destroyed before succeeding, and the First Law doesn't require futile attempts). In the third attempt,.
 * It also shows up in Arthur Conan Doyle's Sherlock Holmes story The Adventure of the Three Garridebs. When a man claiming to be an American lawyer recently arrived in London calls on Holmes, Sherlock first asks whether the American had placed an ad in the "agony columns" and is assured that he did, then when the 'American' says he's from Kansas, Holmes mentions an old correspondent of his, Dr Lysander Starr, who was "mayor of Topeka in 1890." The 'American' assures him that Dr Starr's memory is still honored in Kansas. After he's left, Holmes assures Watson that he's not what he claims - there was no ad in the agony columns and "Dr Lysander Starr" is completely fictional.
 * Also shows up in The Lost World, when Malone is trying to gain Professor Challenger's trust by pretending to be a fellow scientist, Challenger quizzes him on various scientific terms, all of which Malone claims to be familiar with. Challenger then informs him that he had been speaking gibberish and tackles him out the door.
 * In one of Robert Asprin's Phule's Company novels, a Space Legion soldier trying to prove his identity is asked "Who led the Galactic League in free flies last season?" Not only can he not come up with the player's name, he misidentifies the sport—and his comrades conclude that it's really him, because he's known to be completely ignorant about sports.
 * In Haunted, one of the Women of the Otherworld series, Lucas asks "Jaime" if she wants Indian food, confirming Eve's claim that she's been possessed by a demon ghost.
 * Appears in The Light Bearer, a historical-fiction story about the Roman conquest of Germania. Germanic chief Baldemar reveals an imposter to be a foreign spy by asking him if a famous local woman has recovered from an illness, to which he replies that she has—she actually died the previous year.
 * In Aaron Allston's Galatea in 2-D, when Roger suspects the false Donna, he asks if Elsie's at David's, rather than Dylan's.
 * In White Cat, Cassel casually asks his brother Barron if he remembers certain incidents from their childhood, and Barron says he does... except the incidents are things Cassel made up, or that happened to someone else. In this case, though, Barron isn't an impostor; he's and trying to cover it up because
 * This is how, in an early arc of Perry Rhodan, Atlan discovers that the eponymous protagonist has been replaced by a doppleganger . The impostor has most of the original's current knowledge due to his allies telepathically interrogating the former before setting the plot into motion, but Rhodan managed to slip in just enough misinformation about his initial clashes with Atlan for the latter to catch on once the subject comes up. (In their first duel in that museum on Venus, they fought with broadswords, not smallswords, and the imposter then failing to recognize a silly little rhyme that had special meaning for them both after a long, wearying chase on the planet Hellgate cinched it.)
 * In a Nancy Drew book, Nancy has become suspicious of a young man claiming to be the long-lost son of the wealthiest man in town. (The man was presumed dead in an avalanche during a trip to Switzerland but has returned several years later, claiming to have been recuperating in a hospital all this time). While initially charming everyone, he still makes several mistakes—buying his housekeeper a chocolate cake for her birthday when he should know that she's allergic, as she once had a severe reaction in front of him. Nancy finally trips him up by gushing about his 18th birthday party (the last one he had before vanishing), mentioning how cool his "giant purple and white football cake" was. The man enthusiastically agrees—until Nancy coldly informs that that's NOT the kind of cake that was served.
 * In Kurt Steel's The Imposter, the president of an aircraft company, after discovering the dead body of a double who was sent to impersonate him in a Nazi plot but ran afoul of an entirely separate Nazi plot to assassinate said president, decided to pretend to be the double in an attempt to flush out both sets of enemy agents, but was revealed when one of the dead man's more suspicious associates made some comments about things which had never happened.
 * Carpe Jugulum: A vampire tries to get Magrat to open a door by pretending to be Nanny Ogg. Magrat demands that "Nanny" first tell the joke about the old woman, the priest, and the rhinoceros. The vampire tries to protest that this isn't the time for that—proving it's an impostor, since the real Nanny Ogg always has time for a dirty joke.

Live-Action TV
"Martha: Would you like some tea? Jenny: Yes, thanks. Martha: I could put a nice bit of gravy in the pot. And some mutton. Or sardines and jam, how about that? Jenny: I like the sound of that. Martha: Right. Hold on a tick. (discreetly flees)"
 * In the The X-Files episode "Three of a Kind", this is actually used against the Lone Gunmen when Byers is attempting to pass himself off as a defense contractor. One of the other players at the poker table asks him a question: Langley, who has been providing research and info to support Byers' masquerade, comes up empty and tells Byers to fold. Byers, unfortunately, is feeling too bold for his own good, and exposes himself with a blatant lie.
 * Red Dwarf
 * In "Balance of Power", Lister realises that Kochanski is a fake when he refers to them having had sex behind the bins, which they never had.
 * In "Psirens", to differentiate between Lister and a shape-shifting, brain-eating Psiren, the rest of the crew got them each to play the guitar. Lister incorrectly believed himself a guitar god, so the Psiren played excellently. The crew then knew which one to blast. Although after hearing how the real Lister plays, they wanted to shoot him too.
 * Star Trek
 * In the Star Trek the Next Generation episode "The Arsenal of Freedom" a simulacrum of a Starfleet captain uncritically accepts Riker's claim that his ship is called Lollipop ("It's a good ship"). Likewise, in "Allegiance", Picard mentions a recent, still-classified incident in front of a fake Starfleet cadet, knowing that a real one would have no way of recognizing the comment as anything but a meaningless name. In "Conspiracy," an old friend of Picard's does this to Picard because of alien parasites taking over the minds of Starfleet officers, which is explained when Picard asks his old friend what the hell he's talking about.
 * In the Voyager episode "Renaissance Man", Chakotay makes up an incident he claims Janeway told him about. When "Janeway" claims the current crisis has nothing to do with that past one, Chakotay knows that she's a fake. (It was the Doctor being forced to act as The Mole.)
 * In the DS9 episode "Inquisition", while Bashir already suspects that things aren't what they seem, he proves it to himself and his captors when he asks what happened to O'Brien's shoulder, previously injured playing racquetball. O'Brien says it got better; Bashir then says it wasn't dislocated during a racquetball game, but kayaking. Holodeck room appears, Bashir's interrogator congratulates him on seeing through the illusion.
 * Charlie's Angels: In the pilot for the original series, Kelly Garrett (Jaclyn Smith) was masquerading as a long-lost heiress. She met up with Aram Kolegian (Tommy Lee Jones), who had known the heiress before her disappearance. He casually mentioned several things to her about their past which she agreed with. After she left, he said to himself that he didn't know who she was, but she sure wasn't the heiress because the things he had said were lies.
 * Subverted earlier in the episode, when an old friend of the family tries to bluff Kelly with stories of her (well, the girl she's pretending to be) childhood litered with incorrect details. Kelly, however, corrects each mistake and calls him out on what he's doing rather quickly.
 * The Prisoner episode "The Schizoid Man". After a Village agent surgically altered to look like #6 is killed, #6 attempts to masquerade as the agent to escape. Unfortunately, he talks too much and makes several mistakes, causing #2 to become suspicious. #2 mentions someone named Susan saying something "only a month ago": #6 doesn't react. He asks #6 to "give Susan my regards" and #6 agrees. Later, after #6's escape has been foiled, #2 tells him that Susan died a year ago.
 * And depending on which episode order you prefer, there's also #6's reaction to #2's mention of "the General" as if he's talking about a person; another episode is about a supercomputer by that name.
 * Martha uses this on her roommate Jenny in the Doctor Who episode "Human Nature". As it turns out, Jenny has been possessed by an alien lifeform; the alien's responses to Martha's conversation confirm that not only is she not really Jenny, she's not really human.

"Jack: What color dress was your sister wearing when I took her out last night? Daniel-in-Ma'chello-body: I don't have a sister, and if I did, I'd never let her go out with you."
 * Also used by the Doctor
 * In "The Android Invasion" with Tom Baker, the Doctor realizes he's dealing with a Sarah Jane android when she accepts some ginger beer, the real Sarah Jane having told him earlier that she can't stand the stuff.
 * In an episode of Xena: Warrior Princess, Xena identifies a supposed as a  by asking him if he is eager to see the waterfall in his home town again. Of course, there is no waterfall.
 * In The Wire, Chris and Snoop find out which drug dealers are from New York and trying to muscle in on their territory by asking things only someone from Baltimore would know. Unfortunately, Snoop isn't that knowledgeable of local pop culture herself, and after she almost kills someone who gives a correct answer, Chris decides that he should handle asking the questions.
 * Stargate SG-1
 * In an early episode, this was used to determine whether an elderly alien really was Daniel as he claimed he was. (He was)

"Michael: Gustavo, we talked about this on the phone. I'm giving you eight thousand dollars for a file. Part of what that money buys is privacy. Contact: I don't care what I said on the phone. You don't tell me what I want to know, you don't get this file. Eight thousand, no eight thousand. Michael: The deal I made with Gustavo was for ten thousand dollars, not eight thousand dollars. He was very clear about that number. And we never talked on the phone. You wanna tell me who you are?"
 * Played with in "1969", when the team has traveled back in time and are assumed to be spies. Not trusting their American accents, the interrogator asks Daniel, in Russian, if they are spies. Daniel answers "no", but instinctively switches to Russian as well. O'Neill is rightly annoyed.
 * Stargate Atlantis: In the season 5 premiere:.
 * The Middleman: The Middleman is being possessed by an evil genius. Ida, warned by Wendy, innocently asks if there's anything he needs from her before she goes home to her husband and children. The fake Middleman, not knowing that Ida is an android, doesn't suspect a thing.
 * Heroes: When Peter is controlling the body of Jesse, one of the Level 5 villains, Knox, his fellow escapee, catches him this way by asking "Jesse" if he can't wait to see his family in Detroit, when Jesse is from Leeds.
 * One episode of Big Wolf on Campus uses this trope to help the two main protagonists distinguish between who is or isn't possessed by a vengeful ghost out to murder the main hero. When sidekick Merton Dingle is possessed, Tommy Dawkins is able to figure it out after Possessed-Merton fails to remember the secret word that lets them know if he's possessed or not.
 * In an episode of Farscape where Crichton believes he has returned to Earth, the alien masquerading as pulls one of these. In a later episode,, Crichton references that conversation.
 * In Twin Peaks, Audrey Horne is caught out this way when she fakes her resume at One-Eyed Jack's.
 * Burn Notice:


 * There was a subversion early in the series; see below in the subversion section.

"Sam Casey: Sorry about that last bump, Dr. Hale. I hit a hole in the road. Crow: He's mellow but cunning. Abbey: (trapped in the back of the truck) What bump? Sam: I hope it didn't jar you too badly. Dr. Hale: Uh, well it almost knocked my glasses off, but that isn't important. We have to make up that lost time."
 * Alias: It seemed to happen quite a lot, due to all the spies, moles, and infiltrators, but mostly due to Project Helix, an Applied Phlebotinum that allowed one person to be identical to another. Will Tippin held a gun on Sydney Bristow because he thought her to be an impostor. He asked her what he spilled on his shirt a decade ago before a job interview . Similarly, Sydney realized Francine had been killed and replaced with a gene-disguised impostor when she accepted a bite of coffee ice cream, which Francine hated.
 * Knight Rider
 * Michael Knight finds that the villain with Latex Perfection is not Devon by calling him Ishmael, which confuses him. Earlier in the episode, Devon had greeted Knight quoting the beginning of Moby-Dick: "Call me Ishmael".
 * In another episode, when a girlfriend expresses concern about her father's behavior (he's been kidnapped and replaced with an impostor), Michael chats with him about the Disneyland tickets he had supposedly asked him for. When the man responds enthusiatically, Michael and the girl know he's a fake—they had never made any such plans.
 * Family Matters: Urkel is the captive of a man impersonating Carl's partner. Carl hears him talking through the door and not giving the standard reply of, "Not if I see you first," when he says, "See you later." Carl baits the kidnapper by sliding money under the door that he doesn't owe him and breaks it down when he comes to get it, then apprehends the felon.
 * Sanctuary: Will and Helen are among the survivors of a plane crash who are being picked off one by one by a creature that can create visual illusions. They know the creature can make itself appear to be one of the survivors, but they don't know who it is. The creature lures Will out of the plane and takes on his appearance. Helen catches it when, as Will, it offers her a cup of tea and she claims to prefer coffee; the real Will would have known that Helen hates coffee.
 * In Tokusou Sentai Dekaranger, Hoji and a Monster of the Week switch bodies. Ban figures it out by calling Hoji "aibo" (partner). The real Hoji always says "Don't call me 'partner!'" but the villain didn't know that.
 * In the Poirot episode "Hickory Dickory Dock" (not sure if it's also present in the book), one of the students professes to be an expert in Keats. When Poirot quotes some poetry at her she assures him that he certainly knows his Keats. The only problem is that it wasn't a Keats poem.
 * One episode of the 2009 V series has Erica out James May's girlfriend as an undercover V agent using this method. They were engaging in small talk about (among other things) where she went to college, and Erica deliberately referred to the wrong football team, which exposed the alien when she failed to correct the error.
 * Kamen Rider Blade had a variation on this in the Hyper Battle Video, where a Trial has impersonated Kazuma, and subsequently Blade. Hajime roots out the Trial by calling out Kazuma's name; after the battle, he explains that the Trial reacted first because of its superhuman reflexes, to which Kazuma responds "That makes me sound kind of slow, doesn't it?"
 * The Gemini Man: Used by Intersect Agent Sam Casey (also seen in the Mystery Science Theater 3000 episode "Riding With Death," featuring two episodes of the series repackaged as a TV-movie) on Dr. Hale, who is supposed to be in the trailer of the truck Sam is driving, but suspected of being in the helicopter that's been following the truck the entire episode (which he is). Dr. Hale has rewired the intercom in the back of the truck to communicate with a radio unit in the helicopter.

"Frasier: This morning, you said you met him on a double date. Roz: Oh yeah, it was on a double date! Frasier: THIS MORNING YOU SAID NOTHING!"
 * In an episode of Lie to Me, Cal and Torres visit a fertility clinic, posing as a married couple looking for an egg donor. Cal asks if what they've been told is possible, namely that his "wife's" infertility is due to an estrogen imbalance caused by the Coriolis effect, and the doctor agrees that it's a definite possibility. Had he been a real doctor, he would have known that the Coriolis effect has nothing to do with medicine.
 * In an episode of Murder, She Wrote, Jessica becomes suspicious of a man's claim of having been in the armed forces. To that end, Jessica asks if he served in X division with her husband Tom. The man readily claims that he did and describes Tom as a fine soldier and one that he admired and respected. Of course, Jessica knows he's lying as her husband's name was NOT Tom, and he served in a different division of the armed forces than the one she named. However, she doesn't confront him with this, nor reveal it to anyone else, knowing the man could easily Hand Wave it as an honest mistake rather than an outright lie.
 * In another episode, she pulled a similar stunt with a professional chef, asking him about a favorite recipe of hers, claiming it was a pork dish with Bearnaise sauce. This tripped up the chef because the dish in question was actually salmon. The chef was then forced to confess that he did not graduate from cooking school, which tied in with a possible motive for murder at the restaurant where he worked.
 * A case of bluff the witness is used in The Good Wife episode "Unprepared".
 * A storyline on Third Watch had the cops are searching for a pair of rapists who pose as police officers so that they can pull women over and then assault them. At the episodes end, as the fake cops are menacing a woman, the real cops arrive. The fake cops try to claim that the woman's screams for help are just the raving of someone high on drugs. Already suspicious (they know the woman and know she's not an addict), one of the real cops asks the fakers a question in "cop lingo". When he's unable to answer, they instantly know they've caught the criminals.
 * Frasier. Roz discovers she's pregnant, and Frasier encourages her to find the father and tell him the news. She claims one morning at Café Nervosa that the father was an architect, and not much else. Later, at Frasier's apartment, she mentions that he was an archaeologist, and Frasier gets her into the kitchen to pull one of these off the bat by asking her how the two met again.

"Chang: What year were you born? Hurley: 1930. Chang: So you're 47 years old? Hurley: Yeah. Chang: And you fought in the Korean war? Hurley: There's no such thing!"
 * A General Hospital storyline had a woman named Katherine Crawford coming to town, claiming to be friends with the recently deceased Dominique Baldwin and rapidly befriending her widowed husband, Scott after learning that Dominique was dead. However, Scott's friend Lucy was immediately suspicious and began to investigate. Her first discovery, that no one named Charles Crawford had died recently (Katherine was claiming to have been recently widowed herself) was thwarted when Katherine stated that her married name had been Reynolds. But her second attempt proved successful when she was able to present the real Katherine Crawford to Scott. Unfortunately, Scott decided to believe Katherine's lame excuses, leading Lucy to have to make another discovery to prove Katherine's duplicity—upon re-reading the letter than Katherine wrote to Dominique, she realizes that Katherine used her fake name, something that would have been unnecessary if Dominique knew her. Which meant that Katherine ALREADY knew that Dominique was dead before coming to town, and that her intent from day one was to scam Scott out of the money that he'd inherited.
 * A short-lived spy series in the sixties had the hero pull a Dead Person Impersonation of a wealthy man who'd been killed by Soviets when they mistook him for the spy. The rich man's wife caught on to the imposture fairly quickly, because her husband was a Jerkass, and the agent treated her with courtesy. She tested him by asking if he'd consulted his sister about a certain business dealing. Not having had the chance for a proper briefing about the man he posed as, he said dismissively, "What does she have to do with it?" Of course, "My husband doesn't have a sister." She wound up covering for him anyway.
 * Hogan's Heroes: The crew was trying to decide if their most recent addition was truly a POW or a spy. Hogan tells his men not to ask about Ty Cobb's batting average as that's the first thing a spy would learn. Later on after correctly answering questions on American cities, one of the men asks the spy if he knows anything about Ty Cobb, to which the spy asks "Want to know his batting average?"
 * In another episode, one of Hogan's crew is trying to infiltrate a meeting of German officers under guise of another visiting officer. One of them, perhaps sensing an impostor, says he had heard that he injured his hand in a hunting accident, and asks him which hand it was: the right or the left? The spy manages to dodge the question by saying: "Thanks to superior German medical techniques, you can't tell which of my hands was injured!"
 * Artie does this in an episode of Warehouse 13 to prove that Myka is really Alice Liddell, who has somehow swapped with Myka using a disco ball (It Makes Sense in Context).
 * Averted in season 5 of Lost when Pierre Chang realises that Hurley is probably from the future. Hurley blows his cover when he mistakes a straight question for a bluff.


 * Played much less seriously in the pilot of The Chicago Code. Wysocki asks his partner what time the game starts, and Evers tells him 1:20. Wysocki notes that the White Sox have the day off, which blows Evers' cover revealing himself for the traitorous Cubs fan he truly is.
 * On Fringe, Peter eventually uses this on, reciting a line of Greek to her that the genuine article would have recognized. Unfortunately he wasn't very subtle about it, and she was waiting in the next room with a gun.
 * Revenge: Victoria invites the fake Amanda Clarke to tea and serves strawberries. When "Amanda" eats them, Victoria recalls her having had a severe allergic reaction to strawberries as a little girl. "Amanda" claims to have grown out of the allergy, but Victoria now knows she's an impostor because she made up the whole thing.

Radio

 * In the Adventures in Odyssey episode "Sheep's Clothing", a suspicious pastor asks "Paula Jarvis" (who has already slipped a few times) about the annual blueberry festival from where she supposedly grew up. He doesn't mention that they actually grow strawberries there...
 * Novelist and sleuth Paul Temple and his wife Steve sometimes use this to subtly reveal impostors.
 * In Paul Temple and the Gilbert Case, concerned for the safety of his wife, they agree on an arbitrary question/answer which only they will know, and which she can use to challenge any telephone caller claiming to be him. The first use of this is a subversion, but on a subsequent occasion in another series, it's successful in revealing an impostor.
 * In Paul Temple and the Conrad Case, he speaks to Elliot France, another author, over the telephone, and congratulates him on the success of his book 'Zero is Tomorrow' - 'France' thanks him, but the title is actually that of Temple's next, as yet unpublished, novel.
 * In one episode, Steve receives a phone call from a very plausible impostor claiming to be her husband. The only way she knows it isn't him is.

Religion and Mythology

 * Samson uses ruses about his weakness in The Bible.
 * Also, the Gileadite trap for Ephraimite spies in Judges 12. The Ephraimites were unable to pronounce 'sh' properly, so the Gileadites used the word 'shibboleth' as a password- if you couldn't make the sound correctly, and rendered the word 'sibboleth', it was definitely not your lucky day...

Theater

 * In The Bat, Brooks claims to be the new gardener, but does not seem to know that rubeola, alopecia and urticaria are not in fact hardy perennials.

Video Games
"The Wanderer: "Marcus says... shit..." Renesco: "Really? I'm sure he didn't send you all the way down here to say 'shit'.""
 * In Professor Layton and the Curious Village, the protagonists get suspicious about when they find a newspaper article mentioning the man's love for sweets when previously he had violently objected to being served tea and cakes. They question him about this and mention his wife's name... only they give the wrong name, and he proceeds to parrot the mistake, exposing himself as an impostor.
 * Played with in Fallout 2 by Renesco the Rocketman when you're looking for parts. After giving the password, you're asked for the second password - your only response is to cuss out the foreman for not giving you the second password. Renesco then says to relax, that there was no second password. Humorously, if you leave this quest on the backburner for too long, you can forget the first password too...


 * An interesting case in Dragon Quest VI. The Hero enters the castle of (real world) Somnia after discovering you look exactly like the missing prince. The chancellor discovers that you bought noble clothes and he asks the name of your long dead sister,

Web Comics
"Dave: Yes, Lupin of the past, I've long ago solved all your petty problems. Madblood: Ah, good! You can tell me how to correct the degradation of 500th-generation molecular cascade patterns on my liguid-crystal microcircuitry! (beat) Dave: Should I save us some time and admit I'm not actually you? Madblood: That'll do nicely. I have no idea what I just said anyway."
 * Casper uses this on "Komi" in Darken.
 * Girl Genius,
 * Agatha uses this tactic to sound out whether Othar is the real deal. (He is.)
 * Later, the Heterodyne's seneschal Carson von Mekkhan uses a variant on the same trick to test whether Agatha really has a Heterodyne heritage or not. (She does, but her performance fails to entirely convince him.) Eventually Agatha got tired of the questions and started telling him things that only a real Heterodyne should know, which caused him to end the interview and move on to the next stage of confirming her heritage.
 * In General Protection Fault, Nick uses this to confirm whether he's dealing with the real Ki or not shortly after he's been kidnapped.
 * Played with in this Wondermark comic.
 * Basic Instructions recommends this over Kill Us Both when dealing with an Evil Twin, as it has less of a chance of backfiring.
 * In Narbonic, Madblood uses this to prove that the disguised Dave isn't really him from the future.


 * Later on, Helen immediately spots Madblood (disguised as Dave) as an impostor, and decides to mess with his head by pretending she and Dave had an affair, which Madblood is forced to play along with.

Web Original

 * In Defenders of Stan, Butt Monkey Stan has a deathray pointed at two guys. One is his Jerkass brother, Ted, and the other is his brother's evil robot clone. Stan says, "I love you, Ted." The robot clone says that he loves him too while his brother laughs and calls him gay.

Western Animation

 * Hilariously overblown in Fantastic Four: World's Greatest Heroes when shapeshifting aliens are posing as every single one of the heroes' neighbors and acquaintances. Reed Richards starts asking questions like "Do you remember when we first met? Was it... five hundred years ago? On the moon? Remember, you flew up there in your bathtub?" and "I always loved your wings, Mrs. Smith. They're so white and fluffy. Would you show them to me, please?"
 * In The Real Ghostbusters, Egon bluffed a Janine imposter by referring to his mother as his Aunt Helga. The real Janine would recognise Egon's mother because they've met before.
 * In Transformers Prime, Bulkhead thinks there is something off about his friend Wheeljack. He asks him about a certain battle. His friend recites what he did perfectly, except he says that Bulkhead was there, when he was already with Optimus.
 * In the Regular Show Episode Temp Check, a temp that Rigby hires turns out to be a shapeshifter that gradually changes until it's impossible to to distinguish between the two of them. The attempt to get the impostor to expose himself by asking questions fails, so Mordecai offers the winner of the challenge a hug. "Rigby" takes it, which outs him as the impostor (since, earlier in the episode, it's shown that Mordecai and Rigby would never hug one another.)
 * Sonic Sat AM had Sonic bluff a robot imposter of Sally with a long and rather complicated handshake that they tended to use: he changed the last part and when she followed along, he confronted her.

Real Life

 * In World War II, American GIs would use questions like this relating to things like baseball or their buddy's supposed hometown to ferret out German special forces. Woe betide the nerdy soldier who didn't follow baseball well enough to know that Joe DiMaggio wasn't a pitcher, or the British/Commonwealth soldier who had never heard of DiMaggio. Or General Omar Bradley, who spent a couple hours under arrest durring the Battle of the Bulge because a guard insisted that Chicago is the capital of Illinois (Springfield is). This was all pointless, since the Germans could only find 10 people capable of faking an American accent and had already used them up.
 * A variation for those on watch both used and inverted this system: The guard would state "The Land of the Free," to which an American would reply "And the Home of the Brave." Then the guard would state "The Terror of Flight," to which a German would reply as "And the Gloom of the Grave"... Every American soldier would know the first verse of their national anthem, but only a spy trying too hard to pass as one would know the third verse.
 * The Dutch resistance had something similar. One of the main German prisons was at a place called Scheveningen. In German, the "Sch-" cluster is pronounced as a single "sh" sound, where as in Dutch it's an "s" followed by a throaty "ch" (like at the end of "Loch"). So if a resistance fighter suspected a colleague was really a German, they would talk about the prison, and see how they pronounced it.
 * American forces, similarly, would use bizarre codewords like "Lollapalooza" to trip up Japanese-born impostor radio operators who, presumably, could speak passable English but couldn't disguise the R/L confusion from their birth language.
 * El Al security guards ask similar questions of the airline's passengers. For example they might ask if the passenger saw a sporting event that didn't actually happen. If they say "yes" it's a good sign they're hiding something.
 * In Northern Ireland of The Troubles, one possible shibboleth is to ask someone to spell a word containing "H". Protestant schools teach children to say "aitch", Catholic schools teach them "haitch". Not certain which is the original name—some say it's from Latin aka and the H was later added; others that it's from haca and the H was dropped.
 * India-based workers who do tech support for American companies will sometimes have current weather information or sports information up for whatever American city they claim to be in.
 * During the Peasants' Revolt in England in 1381, Londoners went around attacking Flemish weavers who they accused of stealing their jobs (nothing ever changes). If they found a random passer-by, they challenged him to say "bread and cheese", as those words are distinctively twisted by a Flemish accent ("brote and kaas").

Anime and Manga

 * Death Note: L does this to Light quite a bit to see if he slips up by saying something only Kira would know. For example, showing him three suicide notes Light had some criminals write and seeing if he can find the secret message Kira inserted into them to taunt L, who has intentionally given Light the notes in the wrong order. However, Light is also a supergenius, and quickly figures out what L is up to, and hence doesn't expose himself (by putting the notes into the right order or being surprised when L introduces a fake note to the mix). Partially subverted anyway. It takes a bit for Light to realize that the fake note makes sense, and L ends up being slightly more suspicious of Light than he was before the test.
 * In Yu Yu Hakusho the heroes are told that one of them was replaced by an impostor who knows everything about the replaced person making this trope unusable.
 * Though Yusuke still tries asking Botan her three sizes. Because, of course, she'd never told him.
 * In Cat-Eyed Boy, the title character shapeshifts himself into the form of a young boy to tease him. When the mother discovers this, she demands to see a birthmark she claims the boy has, and Cat-Eyed Boy assumes it's an example of this... so is the one of the pair not to have the very real identifying birthmark. Oops.

Films -- Live-Action
"Benedict: You new at the commission? Linus: Been there about two years. Benedict: I know Hal Lindley over there; you work with him at all? Linus: (Beat) Not since he died last year."
 * Knight Rider: In the 2008 movie, Sarah Graiman is accosted by a security guard during her escape from a pursuer. KITT warns her that the guard may in fact be a fake, and Sarah tells the guard about where she was going—except all of the locations she lists don't exist. The guard catches on, however.
 * Terry Benedict tries this on Linus in Ocean's Eleven. For some context: Linus is disguised as a member of the Nevada Gaming Commission, and Benedict is the owner of the casino(s) Linus and co. are trying to rob. It doesn't work, since.


 * In Catch Me If You Can, Frank (posing as a lawyer) claims to have been taught by a professor who also taught his girlfriend's father, and her father asks what the dog's name was. Frank, smelling a trap, replies simply that the dog had since died. The father remains suspicious.
 * In Kingdom of Heaven, when Balian meets his father's knights, one of them tries to discern if he really is his son. After mentioning the height, the knight goes on about the eye color of his liege, which is promptly corrected by Balian, thereby proving that he did not Did Not Do the Research, at least.
 * In Die Hard, John encounters Hans alone on one of the upper floors. Hans quickly pretends to be an escaped hostage, speaking in a convincing American accent instead of his usual British (well, German-ish). John introduces himself, and Hans gives a name that John checks against a nearby office directory. In this case, Crazy Prepared Hans gave a name from the directory.
 * John wasn't actually that convinced by the accent, since it sounded too state-neutral to be real. John says it sounded like he should be on television with it.

Literature

 * Discworld
 * Interesting Times: Rincewind, trying to hide his foreign origins on the highly-xenophobic Counterweight Continent, is asked by a suspicious restaurateur about a specific man on a specific road. He quickly declares he's never heard of the man or the road... only to find out the man is a high-ranking government official that everyone would need to deal with and the road is the main street through the capitol. It works out, however, as the restaurateur is the local equivalent to CMOT Dibbler and is quite pleased to meet a foreigner.
 * In Night Watch, Vimes has to impersonate his (now dead) mentor John Keel in the past. His knowledge of Keel, combined with his knowledge of the events at the time and some information from the Monks of History, lets him answer the interrogating officer's questions better than the officer himself could.
 * The interrogator assumed that the imposter is a criminal, so he starts off with questions meant to trip up a civilian and not someone who actually served as a policeman during that time. Before he can try more personal questions Vimes has him so browbeat that he does not realize that Vimes says the wrong amount when speaking of his promised wages. Vimes uses this to get more pay and a higher rank.
 * In Jean M Auel's Earth's Children books, Ayla is asked about the leader of the Mamutoi tribe which she tells them she has been adopted into, but she knows the fake name (Lutie) for what it is and gives the correct information ("Tulie").
 * In a Marlowe book, when a woman is giving a confession that Marlowe doubts, she talks of dumping a man's body in a reservoir and Marlowe asks her how she got it over the fence. She blusters about adrenaline and then Marlowe reveals that there is no fence. After she breaks down he admits that he's never been there and really doesn't know about fence or no fence. He just thought she was lying.
 * In Stephen Fry's Making History, the agents try to crack Michael's story by asking him if the man he claimed to see on a train had a white or gray beard. He says that the man was clean-shaven, which turns out to be the correct answer.
 * In Isaac Asimov's The Union Club Mysteries, the protagonist subtly interrogates a possible spy by playing a word-match game. After several iterations, the protagonist uses a phrase from the third verse of "The Star-Spangled Banner"; the spy promptly gives the phrase that immediately follows it. The protagonist concludes that, since real Americans only know the first verse (except himself, because he knows everything), the other man is actually a spy who was trained a little too well.
 * Asimov was a huge proponent of knowing the entire National Anthem.
 * In Trainspotting, at a job interview Renton claims to have gone to a posh secondary school, which the interviewer also went to. The interviewer then asks him if a particular teacher is still teaching there. Renton, sensing a trap, simply laughs and says "God, you're taking me back now!"

Live-Action TV
"Quentin: Paco... man. He still make that pruno? I did a couple of months with him in county and man, he made the best prison wine. Michael: Paco doesn't drink. What are you trying to pull?"
 * In an early episode of Burn Notice, Michael Westen gets close to a target by claiming they had a mutual former cellmate in prison. Michael figures out the target is applying this trope to him.

"Servo: Damn, you are me!"
 * Later, talking to Sam, he admits he guessed and was lucky to have been right.
 * Done in Mystery Science Theater 3000: when Tom Servo's evil pod clone shows up, Crow tries to discern which Servo is the real one by asking about the type of condiment Crow poured into his shoes—despite Servo having no feet—the previous week. The real Servo forgot, and the fake one correctly guesses "Was it... Ketchup?"

"Crow: Frankly, I don't see why we need any Servo at all"
 * Mike pulls it off by asking about Servo's collection of boxer shorts. Pod!Servo thinks this is another trick, until Servo rattles off his entire inventory in enough detail to drive the clone away in fear and "self"-loathing.


 * In Prison Break, Charles' first conversation with Michael is along these lines when Michael claims to have known his wife, but fails to trip him up.
 * There was a scene, possibly from the short-lived '90s TV series Probe, in which the hero is trying to figure out which of two men is a Soviet spy, by quizzing them about obscure sports trivia. He unmasks the spy because the guy had prepped too thoroughly for his mission and was too knowledgeable.
 * Subverted in Supernatural, when a shapeshifter imitating Dean gives Sam the correct response.
 * In Medium, when Ariel's body is possessed by the spirit of a murdered woman, Joe tries to pull this trope by suggesting an idea for her birthday party, and deliberately giving the wrong month. However, the woman in Ariel's body is prepared by now (not in the least because in a fit of desperation, Allison suggested, in front of "Ariel", that Joe ask her something only the real Ariel would know) and knows when Ariel's real birthday is (presumably from looking at her student ID). She calls him on his error, and he covers up by claiming that it's hard to keep track of everyone's birthday when you have three kids.
 * Leverage: Sophie is nearly outed when the mark asks her if she's familiar with a certain person. Nate smiles and tells her (on her earpiece) to reply that the man is dead, which satisfies the mark. This is a bluff on Nate's part, though, as Hardison only confirmed the information several seconds later, which would've been too late for Sophie.
 * Blackadder Goes Forth: Blackadder does this when hunting a German spy in WWI. He unmasks the spy by asking the suspect if her boyfriend had been to one of the great universities: Oxford, Cambridge, or Hull. Any real Briton would have known that only two of those are great Universities—as General Melchett remarks, "That's right! Oxford's a complete dump!" Anyway, it goes fine until it's revealed that the suspect wasn't the spy after all.

Radio

 * In Paul Temple and the Gilbert Case, Temple and his wife agree on a question/answer which only they will know, and which she can use to challenge any telephone caller claiming to be him. Unfortunately, . When 'Temple' next telephones, 'he' even goes so far as to remind her to use the secret question, which is then answered correctly.

Video Games

 * In Baldur's Gate, there is a quest that involves the player character doing investigations for Aldeth Sashenstar in his offices under the pretense of being his childhood friend. One of his business partners whose behaviour you are there to investigate (and who is himself in fact a doppleganger impostor) asks you whether, if you were Aldeth's childhood friend, you were friends with Dabron as well. Since Dabron is in truth Aldeth's real brother, it's showing ignorance that will give you away at this point, not that it makes a difference for the plot. It's not clear whether this is intended as a subversion, since the doppleganger could simply be straightforwardly trying to catch you not knowing what it's talking about... but trying to be too Genre Savvy here will certainly backfire.

Western Animation
"Impostor: Actually, we're from the Eastern fleet. We have orders to deliver some cargo. Commander: Ah, Eastern fleet. (sarcastically) Well, nice of Admiral Chan to let us know he was sending one of his ships our way. Impostor: I'm sure Admiral Chan meant no disrespect, sir. (the commander accepts this; but later...) Commander's aide: Sir, Admiral Chan has been on leave for two months at Ember Island. Commander: What?! Why doesn't anyone ever tell me anything?"
 * In the SpongeBob SquarePants episode "Imitation Krabs", SpongeBob quizzes Mr. Krabs and an obvious robot impostor on things "only the really real Mr. Krabs would know". The impostor (who is obsessed with Mr. Krabs, never mind that the questions are things like "How much does a Krabby Patty cost?") jumps in with the right answer on the first two questions, while Mr. Krabs fails on the third.
 * Doesn't help that the last question is completely bizarre and nearly impossible to follow. Of course, it is SpongeBob.
 * Avatar: The Last Airbender has a hilarious Double Subversion in "The Awakening":