Something Only They Would Say

"Wolverine: Wait, it's me.

Cyclops: Prove it.

Wolverine: You're a dick.

Beat

Cyclops: Okay."

- X-Men

The polar opposite of a Not Himself or Something They Would Never Say; a character in disguise or otherwise hidden reveals himself to friends through saying something only he or she would say.

Undercover agents and victims of a Freaky Friday Flip will occasionally use Something Only They Would Say to positively identify themselves. Also handy in figuring out which twin is the Evil Twin, or when you're in the middle of a Twin Switch (though just as often, it's keyed off of Something They Would Never Say).

This is occasionally a "whoops" moment on the part of the speaker: they wanted to remain unidentified but say the identifying phrase out of habit, which at best makes someone just a touch suspicious.

Compare You Just Told Me, Trust Password, Ironic Echo, Cover Identity Anomaly and Bluff the Impostor. No One Else Is That Dumb is a Sub-Trope.

Anime and Manga

 * When Urd splits into good and evil parts, she actually does this to herself, saying "if you're the real Urd, you should know where Keiichi has his dirty magazines, etc." Followed by answering those questions.
 * Cool Old Guy Joseph Joestar is forced to rely on this in the final chapter of Jojo's Bizarre Adventure Part 3. After  As Jotaro puts it. "Only you would know such stupid things".
 * Used as a red herring in Detective Conan, where
 * Played with much earlier in the series, in episode 2: Conan reveals he knows about the mole on Agasa's butt to try to convince Agasa he's really Shinichi in a kid's body--but Agasa just assumes Shinichi's been blabbing. Then Conan uses a Sherlock Scan to demonstrate that he really is Shinichi.
 * In an early episode of Yu Yu Hakusho, Yusuke's deceased spirit possesses Kuwabara's body to tell Keiko that he's coming back to life soon, so he needs her to take care of his body. She refuses to listen to him, so he suggestively compliments her "Nice skirt!" (a callback to a scene in the first episode where he flipped her skirt) and grabs her breasts. This causes her to slap him across the face while shouting "Yusuke, you jerk!" out of habit. Since that wouldn't fly outside of Adult Swim, the Bowdlerised Toonami version cuts out the boob-grabbing.
 * In Baccano, Rachel and her associates at the Daily Days figure out that the Rail Tracer was actually
 * Later, Claire Stanfield reveals himself to Rachel as by making a comment about her ticket purchases.
 * You know how that demon that started the whole thing is always saying "maa, ii"/"well, no matter"?
 * In Sailor Moon, Chibi-Usa knows that a monster disguised as her mother is a fake, because her mother calls her "Small Lady," not "Rabbit," which is the Black Moon clan's name for her. A similar situation occurs in the Sailor Moon Another Story game, where Nergal disguised as Sailor Pluto is given away because she calls Chibi-Usa "Princess," while Sailor Pluto would normally use the same "Small Lady" nickname.
 * Also in one of the final episodes of Sailor Moon S, Mistress Nine reverts to using Hotaru's regular body to get SM to give her the Holy Grail (the "Purity Chalice" in the U.S. TV broadcast version). When SM finds her among the ruins of the Mugen Academy, she realises the person she is talking to is not Hotaru when the latter calls her by her civilian name, Usagi (the real Hotaru never knew her identity).
 * Pretty Guardian Sailor Moon has a great, if narmy, scene, where Sailor Moon exhausts herself trying to protect Tuxedo Kamen and nearly falls down the stairs. Tuxedo Kamen catches her and asks if she's an idiot. SM automatically retorts with "who are you calling an idiot" before realizing their dialogue mirrors the one between her and Mamoru after the latter saved her from being run over by a car. Cue dramatic unmasking.
 * In both the Visual Novel and anime of Fate Stay Night, Archer says and does things occasionally that hint at his true identity.

"Hawkeye: "When it's just the two of us, the Colonel calls me by my first name."
 * In Fullmetal Alchemist, Edward and Ling are wary of one another since either one could be the impostor Envy. Ling proves himself to Edward by offering to recite, in perfect order, all of the items on the room service menu from the hotel where they were staying. He then starts to press Ed's Berserk Button by making a reference to his shortness; when Ed pitches his characteristic tantrum, Ling knows he's the real thing.
 * Later on after Greed's Anti-Heroic BSOD Ed discovers Ling in the hut they used as a fallback after Mustang's guys, the Elrics, and Ling's party worked together to capture Gluttony (interestingly the last place in the normal world Ling was seen alive, really, since the two of them got to Father's base by way of Gluttony's stomach) and Ling's falling over and asking for food is taken by Ed as a sign that it's really him.
 * Played with fantastically towards the grand finale, when Hawkeye expertly uses this to her advantage against Envy when they get split off during Mustang's Roaring Rampage of Revenge.

Envy: *changes back to his normal form* "So the two of you have that kind of relation-"

Hawkeye: "I Lied." *shoots him* "But it was very nice of you to fall for it, Envy.""


 * Akumetsu's mask in the eponymous series really isn't that good for concealing his identity, what with leaving much of his face including his distinctive hair and eyebrows and most of his grin visible, but it's by his 'ya know' that our initial viewpoint character recognizes him in the first arc. When he comes in and coincidentally kicks off his terrorist career by chopping up the Dirty Old Man who'd just hired her in her new career as a teen prostitute with an axe. They're both normal high school students again the next day. (Her for real, him only apparently.)
 * Of course, he doesn't care all that much if he's recognized, since Akumetsu has a policy of dying on the job and
 * The scene gets a callback later, though, with one of the not-important-and-enough-to-be-targetted minion with the underwear on his head tracking the girl down because she said 'Shou!' when Akumetsu came in and said his Catch Phrase.
 * In the final episode of Durarara, Mikado guesses that someone in a chatroom is Kida. The response?
 * Happens with Tetsuya in Metal Fight Beyblade. He wears a (actually very convincing) disguise to try and steal all of Ginga's beypoints, but is recognized at the last minute because of his alias 'Nigel Crabbypants'. Being openly obsessed with crabs does have a downside! Who knew?
 * In Soul Eater, when Maka first shows up in the black room, Soul wonders if she's just an image created by the Little Demon. Her response is to hit him over the head with a book, something only she would do. After that, he admits that "Yeah, it's Maka."

Comic Books

 * The Crow: "It can't rain all the time."
 * Daredevil: in the first appearance of DD's ex-girlfriend Elektra, he reveals his identity when he addresses her by his old nickname for her.
 * In the original WITCH comics, Taranee gets captured and tortured by Elyon and convinced that anything she sees is an illusion. When Will comes to retrieve her, Elyon tries to convince Taranee that rescuing Will is an illusion created by her too. But Will says that she's telling the truth and Taranee can read Will's mind if she wants to verify, and Taranee figures it out because Elyon never knew Taranee could read minds.
 * In Nightwing: Year One, Dick confronts Commissioner Gordon for the first time in his new guise as Nightwing. After Gordon prompts him to "say something only the kid would say" to prove his identity, Dick struggles for a bit before declaring "Holy Mistaken Identity!"
 * In The Return of Superman, Lois Lane asks one claimant to the name Superman why she should give him the time of day. His answer? "To Kill a Mockingbird".
 * In the Donald Duck story "Kappa! Kappa! Kappa!", Donald's nephews see what looks like a famous, ancient Samurai show up to save kappa from the villainous tengu. They quickly realize the samurai is just Donald Duck in disguise... after they see him running away in panic in Donald's distinctive way.
 * In one early The Flash story (during Barry Allen's tenure in the costume, pre-Crisis), this nearly gets Barry in trouble when, while in costume and conversing with a crime scene investigator, he gives the guy a wink that only Barry (as a police scientist) would give him whenever in agreement about something. Naturally, the other cop starts putting two and two together, but Barry manages to convince him by the end of the story that he and Flash are definitely not the same person.

Film
"Bruce/Batman: It's not who I am underneath, but what I do that defines me."
 * The phrase "As you wish" in The Princess Bride. Westley, Buttercup's love, has been presumed killed, (This leads to a My God, What Have I Done? moment for Buttercup. She and   both get better.)
 * In the X-Men movie, Wolverine has just dispatched the shapeshifting Mystique and is confronted by a suspicious Cyclops, leading to the page quote above. Apparently, that little exchange wasn't in the original script -- the actors ad-libbed it, and everyone liked it so much that they kept it.
 * In Harry Potter and The Goblet of Fire,, nearly blows his cover when he performs a familiar facial tic in front of his father.
 * The Batman films use this trope often:
 * In Batman Begins, after being asked who he was under the mask, Batman subtly reveals his secret identity to Rachel Dawes by mirroring a statement that she made to Bruce Wayne earlier in the film, when she caught him in public playing up his Rich Idiot With No Day Job persona and he tried telling her that that wasn't the real him.

"Batman/Selina: Mistletoe can be deadly if you eat it.
 * In Batman Returns, Bruce Wayne and Selina Kyle accidentally expose their identities as Batman and Catwoman to each other by unthinkingly reenacting a snippet of banter from their previous fight. In a slight variation, they switched lines in and out of costume.

Catwoman/Bruce: But a kiss can be even deadlier... if you mean it."

"Jack Napier/Joker: You ever dance with the devil in the pale moonlight?"
 * And this trope is also used in the 1989 Batman film and is how Bruce realizes the Joker is the thug who killed his parents. He repeats the phrase to Joker at the beginning of their final confrontation just before decking him.

"Batman: You killed my parents.
 * Let's not forget

Joker: What are you talking about?

Batman: I made you, but you made me first."

"Robo: Dead or alive, you're coming with me.
 * The Matrix Revolutions:
 * Bane (who's reveals himself to Neo by addressing him as "Mr. Anderson". Neo is slow to catch on, if only because of how inconceivable it is to believe.
 * Happens again in the final battle when Smith says, "Everything that has a beginning has an end, Neo" -- revealing that the Oracle is still in there somewhere.
 * It's interesting to note that from Smith's own perspective, it's the polar opposite trope, Something They Would Never Say. Recognizing that he'd already had a vision of the events playing out before him, he tries to recall what it is he says next, and then says the above words. This at first mildly confuses him and then leads to him completely freaking out.
 * From Ghost: the word "ditto", which Patrick Swayze's character would use to respond to "I love you", to the point where his widow refuses to believe it's him when he tells her those three words through a medium.
 * In Disney's Aladdin, Jasmine is tipped off to Prince Ali's identity with his "Do You Trust Me?"
 * He also rolls an apple down his arm and throws it to her with his elbow; a trick he does as both Aladdin and Prince Ali. The animator who drew Jasmine's facial expression when she realizes this deserves an award.
 * In The Italian Job, the villain realizes that he's on a date with the daughter of the man he killed years ago when she uses her father's trademark phrase, "I trust everyone; I just don't trust the devil inside them."
 * The movie Face Off uses a physical gesture of affection in this way.
 * In Indiana Jones and The Kingdom of The Crystal Skull, a character tries ab As You Wish, which fails..
 * In T2: Judgment Day, the reprogrammed T-800 identifies itself as sent by the future John Connor to help by saying "come with me if you want to live," the first thing Kyle Reese said to Sarah Connor.
 * The same exact scene plays out in T3: Rise of the Machines.
 * And the first episode of The Sarah Connor Chronicles.
 * In the James Bond movie The World Is Not Enough,
 * Happens twice in the first Robocop film, one of which is non-verbal. Lewis initially recognizes Robo as Murphy when he spins his pistol by its trigger guard in the precinct firing range. Later, Robo confronts one of Boddicker's gang members and repeats the same line with which he tried to arrest the goon the first time around, which freaks him out to no end.

Emil: (disbelieving) Wait a minute, I know you... you're dead. We killed you. We killed you! WE KILLED YOU!!"


 * A version of this occurs in in Disney's Condorman, although it's not so much about identity as intent. Natalia and Woody (the titular hero) are sharing a moment together when he says the line, "I'll bring the dip if you bring the Dostoyevsky." Later, when it appears that she has changed her mind about defecting, she says it back to him, which prompts him to realize that she wants to be rescued after all.
 * Syndrome in The Incredibles tells Mr. Incredible "I am your biggest fan...", which makes Mr. Incredible realize Syndrome is actually.
 * In Spies Lies And Naked Thighs, a man is introduced as a secret agent who has been surgically altered to resemble an old friend of the main characters in order to stop an assassination attempt on two world leaders. Late in the film, one character who knows that the assassin is hiding nearby manages to tip him off with a signal from college which meant "There's a girl in the room", revealing that this agent is really the old friend.
 * In Megamind, everyone calls the setting Metro City except for the title character, who pronounces it to rhyme with atrocity. When he's, he accidentally gives himself away when he mentions the city's name.
 * Played with in The League of Extraordinary Gentlemen, after the Big Bad and The Mole have just attempted to destroy the Nautilus with planted explosives. The Reverse Mole, who has stowed away on the escape vessel with the bad guys, manages to send a message to the rest of the League with the coordinates of the escape route. They realize it's from him because of the way the message opens -- he's the only one in the world who would address them collectively as "my freaky darlings."

Literature
": You will go to the Dagobah System. There you will learn from Yoda, the Jedi Master who instructed me."
 * In Eldest, the 2nd book of the Inheritance Cycle, Eragon recognizes the dragon rider in steel armor as his when he spins his hand-and-a-half sword at his hip, much like he did when the two of them trained together.
 * "Jane Smith" was identified by her bizarre taunt ("Rub a monkey's tummy! Rub a monkey's tummy with your head!") in the children's book Wayside School Gets a Little Stranger.
 * In Harry Potter, the good guys
 * In the same book, Voldemort jinxes his own name so that whoever says it is immediately found. That's because only the real leaders of the war against Voldemort would say his name rather than referring to him by euphamisms or "the Dark Lord".
 * Then there's the passwords the Ministry suggested everyone set to identify impersonators. Mrs. Weasley's password to her husband was her husband's pet name for her; the embarrassing/adorable "Mollywobbles".
 * In the light novel The Disappearance of Haruhi Suzumiya (volume 4),
 * This was used time after time in Sweet Valley High, because of all the Twin Switches that were going on. In one example, the twins' friends prove which twin is which by asking Jessica to spell thief and asking Elizabeth who a certain soap star is. Jess spells it wrong and Elizabeth doesn't have a clue about the soap star. Somehow, their friends are convinced...
 * In Stone of Tears, the phrase "true as toasted toads" is used to positively identify a messenger as having come from Zedd.
 * Also subverted in the first book. Richard finds himself under the effects of an "Enemy Web", where people would perceive him as their enemy; Darken Rahl if they're Richard's ally, or as Richard if they were allied with Rahl. Richard sneaks into his brother's tent, gets his attention, and goes to do the the "Loser's Salute," which his brother forced him to do whenever he lost one of their play swordfights as kids, to identify himself.
 * In the last book,
 * In Lord of the Rings, Aragorn quotes to Frodo a bit of poetry that Bilbo wrote about him. Note that Frodo knew the poem not from Bilbo, but because it was in a letter from Gandalf that he (Frodo) was reading right then. Aragorn did not know that the poem was in the letter.
 * In Body Parts by Michael Bates, the tip off is the way a girl says "dif&Atilde;&shy;cil" just as the protagonist's friend used to before she went missing. What's it a tip off to? The fact that the girl was sewn together from body parts harvested from local kidnapped teens, including said friend, which (somehow) gives her an unconscious retention of their mannerisms. This is a bit different from the usual As You Wish, as the girl herself doesn't know the identities of her "donors".
 * In The Stars My Destination by Alfred Bester, Saul Dagenham recognizes a disguised Gully Foyle when he uses a pseudonym that Dagenham had implanted in Foyle's mind back when he first attempted to interrogate him via hypnosis.
 * In Kushiel's Mercy, even though Sidonie's under the influence of Fake Memories wiping out the memory of her boyfriend Imriel, and Imriel himself is a Manchurian Agent, the use of the word "always" when it comes up in conversation always triggers something for them, which they eventually figure out. (Note that "always" is NOT the trigger to unlock Imriel's true personality, but it seems to help the two blend together.)
 * In Unicorn Point, Bane accidentally reveals himself when he speaks a Phaze dialect in place of Mach's Proton-speak.
 * In Xanth there is a Sorceress who likes to possess people. Unfortunately, she often gives herself away by calling people "my pet". Also, the Demoness Metria is described as being easily recognizable, no matter what form she takes, because of her speech impediment (luckily, her alternate personalities have no such speech problems).
 * Played for laughs in The Culture novel Matter. When an Upperclass Twit-turned-fugitive seeks help from his former tutor, the latter tests his identity through several questions, all of which he gets wrong. The tutor wearily concludes this is indeed his inept student of old.
 * Star Trek New Frontier, "Treason": Si Cwan (a ghost) proves he's possessed his sister by fighting both Xyon and Calhoun (neither slouches in the fight department), beating Xyon and getting beat by Calhoun, but proving himself enough for Calhoun to call him "Cwan, you pompous ass!"
 * A variation in The Paths Of The Dead: Tazendra (now a Lavode) is standing guard at Dzur Mountain when Piro and Kytraan arrive to see Sethra Lavode. Being Tazendra, she's ready to just jump down and attack them, but when she hears Piro use the exclamation "Cha!" she recognizes it not as Piro's Catch Phrase, but as his father's, and she's happy to escort her old friend's son in.
 * In the Dale Brown novel Flight of the Old Dog, Brad Elliot recognises a colonel at the Alaskan base the Old Dog crew are trying to get a tanker from and uses a few choice insults to identify himself.
 * In Mark Billingham's novel Lifeless, the man
 * In the Gaunts Ghosts novel Blood Pact, Tona identifies that she's from Gaunt with a message to  by reminding the latter that he lied about his father to Gaunt on the first day of scholam.
 * In the Elenium trilogy by David Eddings, Sparhawk and other members of the Pandion order of knights have a long-standing code to identify themselves to one another. When traveling in disguise, Sparhawk sends a messenger to the home of a brother Pandion with the message that he "has brought his little mother for a visit." Little mother is the Pandions' Term Of Endearment for Sephrenia, their tutor in magic. (She happens to be present for the dispatch, and is surprised to learn of the code in her honor.)
 * A book in the Goosebumps series is about an evil pet shop that turns children into animals and sells them as pets. The protagonist has a friend who can do somersaults. At the end of the book she gets a pet dog. Whe it stands up and does a somersault, she realizes who it is...
 * In The Dresden Files novel Ghost Story, Molly asks to prove it's not some supernatural nasty in disguise.


 * In the Liavek story, "A Well-Made Plan", a Body Swapped character shows up at his front door and tries to convince his butler that it's really him. The butler asks what the item that is the source of his magical power is, and the character explodes in fury, refusing to reveal it, particularly since he'd never told the butler in the first place. This is the response that the butler was looking for, and he gladly lets him in.
 * In the Discworld book The Truth, Edward recognizes the Big Bad by a phrase he commonly used, "A lie can run around the world before the truth has got its boots on."

Live Action TV
"Giles: How did you know it was me?
 * In one of the most brutal subversions of this, in Star Trek the Next Generation, the completely altered Jean-Luc Picard, aka Locutus, addresses the Enterprise crew after their failed attempt to destroy them. "Your resistance is hopeless... Number One." The look on Riker's face, and the crew's, was pure Oh Shit!!.
 * To clarify, The Reveal here is that Locutus--and therefore the Borg--had access to all Picard's memories, and therefore knew all the Federation's plans to try and defeat the Borg.
 * In the Buffy the Vampire Slayer episode Dead Man's Party, Cordelia asks, "How do we know it's really you and not zombie Giles?", to which Giles responds, "Cordelia, do stop being tiresome," and Cordelia quips, "It's him."
 * Also, when Giles is turned into a demon in A New Man, nobody but Spike is able to understand his grunts. However, just before she's about to kill demon!Giles, Buffy recognizes him. After Giles is turned back to human, she gives the following explanation:

Buffy: Your eyes. You're the only person in the world that can look that annoyed with me."

"Buffy: Giles, it's me, and I can prove it. Ask me something only Buffy would know.
 * In the fourth season, Faith attacks Buffy in her home and activates a magical device during the ensuing fight. Afterwards Joyce asks her daughter if she's all right, and "Buffy" answers with Faith's Catch Phrase ("I'm five by five"), letting the viewer know that a body switch has taken place. Later on in the episode, Buffy (in Faith's body) makes reference to the aforementioned episode of Giles-turned-Demon to prove Giles it's really her.
 * But not before playing with the idea:

Giles: ...who's President?

Buffy: We're checking for Buffy, Giles, not a concussion."

"Daniel: Jack. Are you you?
 * Similarly, in the fourth season of Angel, Angel realises that  when both use the endearment 'my sweet'.
 * In Lost, The Man in Black is inhabiting John Locke's body; when he meets Richard, he says to him: "Hello, Richard. It's good to see you out of those chains," recalling a conversation the two had centuries earlier when Richard was chained to the walls of the Black Rock.
 * In the second season, where Desmond is identified by his use of "brother."
 * Happened in the previous season with the whole Red Sox thing that Sawyer hears Jack say (Sawyer heard it before from Jack's father, that even mentioned that felt bad and wanted to call his son).
 * Doctor Who: in "The Christmas Invasion" and the Children In Need mini-scene that leads up to it, the new Doctor demonstrates himself to be the same man as his previous incarnation by repeating to people the first thing he said when he met them in his previous body.
 * The episode "Midnight" had a strange "detect the enemy" variant on this:
 * "Turn Left" has the reappearance of "Bad Wolf" (series one's Arc Words) as a message from Rose to the Doctor, letting him know that holes must be opening between their parallel universes, which is very very bad.
 * River Song has her personal way of calling the Doctor for help- Graffitiing a singnificant historical artifact with her current Space/Time coordinates, along with "Hello Sweetie".
 * In "The Enemy Of The World", the Second Doctor intends to prove to his companions that he's not the Identical Stranger villain Salamander by playing his recorder ... only he left it in the TARDIS, so he mimes playing it.
 * The Outer Limits TOS episode "The Architects of Fear" features a poignant example. A man volunteers for a mission to be turned into an alien-like creature, climb inside a fake UFO and launch an "attack" against the earth. (All this as part of a plan by a shadowy organization to bring about world peace by uniting humanity against an external threat.) The plan goes awry however, when the "UFO" crashes and the grotesque "alein" is shot by hunters. The man's pregnant wife (who knows nothing about the mission) arrives on the crash scene and doesn't recognize the ship's alien-looking occupant as her husband--until he does a special pointing gesture that has special meaning for the two of them, just before he dies of his wounds.
 * In the Stargate SG-1 episode "Crystal Skull", Daniel Jackson is shifted into another dimension that makes him invisible to everyone but his grandfather, who unfortunately is known to be slightly insane. Daniel instructs his grandfather to repeat some things after him to convince his team that he is standing right there with them. Daniel's frustration mounts as Jack refuses to believe his grandfather, to the point where he shouts, "Jack, don't be an ass!" which of course grandpa repeats word for word. Jack is taken aback and after a second he replies, "Daniel?"
 * The situation is reversed in the episode "Fragile Balance" where an infuriated "Daniel!" from a considerably younger version of Jack is taken as confirmation of his identity by Daniel (the two characters usually adopt a particular tone when speaking to each other).
 * The actor who played Young Jack should have gotten an award for the brilliant job he did of mimicking O'Neill's mannerisms and speech patterns.
 * The trope is lightly mocked in the episode "Spirits", where they encounter shapeshifting aliens:

O'Neill: Yes. Are you?

Daniel: What?

O'Neill: Never mind."

"Daniel: Don't shoot! Just let them tend to Xe'ls.
 * And again:

Jack: How do I know you're the real Daniel?

Daniel: ......... because.

Jack: ... Yeah, okay. (lowers gun)"

"Hammond: How did it go, colonel?
 * The second season episode "Holiday" also had a large dose of this. For example, when Jack and Teal'c have switched bodies:

O'Neill: It did not go well, General Hammond.

Teal'c: Ya think?"

"Michael: No, no, don't buy it. I'm taking my son to the cabin, and there's nothing you can say to make me believe that you are not my father.
 * The ancient communication stones used in Stargate Universe seem to be setting up for a whole swath of this trope. The stones allow faster than light communication through the simple expedient of swapping bodies with the host receiver at the other end. It kicked off in episode 9 with one of the crew being allowed to visit her girlfriend/lover back on Earth, but doing so in the guise of a totally different body. Asked if it was really her, the [blue eyed, Anglo] stranger replied in fluent Cantonese "Have you thrown away that ugly red chair yet?", which satisfied her lover as to her identity.
 * In Living Color parodies this in its fake trailer for Ghost 2 . When Sammy Davis Jr.'s ghost tells the medium to relay to his wife he loves her, the wife says "Sammy would never say it like that". When faux-Whoopi tells her "Sh-Boing-Boing-Boooooiiiing", his wife instantly knows his spirit is there.
 * In The Sarah Connor Chronicles, being a Terminator Spin-Off, "come with me if you want to live" is how Cameron identifies herself to John.
 * Conan O'Brien's Saturday Night Live sketch about Moleculo (THE MOLECULAR MAAAN!) has a superhero keep blowing his Secret Identity this way.
 * A character's missed As You Wish was used in one episode of Family Matters, an episode that saw Steve Urkel bust a criminal and receive a death threat from his brother. This results in Carl and a fellow cop taking shifts in protecting Steve. For years, Carl had always said, "See you later," to that particular partner, who would always reply, "Not if I see you first." Later in the episode, when Carl left his watch, the "buddy" turned out to be the killer in disguise, but as he's about to kill Steve, Carl busts in with the police force and arrests him. As it turns out, the killer replied to Carl with a simple, "Yeah, see ya," letting Carl instantly know it wasn't him.
 * In an episode of Wings, Brian is caught in a bank robbery and hears the masked robber use the unusual phrase, "We'll all be sitting in butter!" Later, as he flies an unknown client back to the mainland, the client uses the same phrase, cluing Brian in to the fact that he's transporting the robber.
 * On Arrested Development, when Oscar has to convince Michael that he's not his twin brother George Senior:

Oscar: I understand. Your child comes first.

Michael: Oh, my God, you're Oscar."

"GOB: Mother?
 * When Buster is pretending to be George Senior and refers to Lucille as "mother":

Buster: I mean lover. I love making love to mother. I mean lover."

"Blackadder: From this moment he was doomed. For you see, the prince is a master of disguise, while Nursie is an insane old woman with an udder fixation."
 * Subverted on The Middleman, when Wendy asks MM this and he refuses to divulge secrets through a civilian interpreter. That's good enough to prove it for Wendy.
 * Interesting variation in the final episode of Black Adder II. Blackadder has apparently sold out Queen Elizabeth to a master of disguise for a single key bit of information--in this case, Nursie's habit of dressing up as a cow at dress-up parties.

"Mulder (as Morris): I'm Mulder. I'm really Mulder. I switched bodies, places, identities with this man Morris Fletcher the man that you think is Mulder, but he's not. Of course you don't believe me. Why was I expecting anything different? Your full name is Dana Katherine Scully. Your badge number is... Hell! I don't know your badge number. Your mother's name is Margaret. Your brother's name is Bill Jr. He's in the Navy and he hates me. Lately, for lunch, you've been having this six-ounce cup of yogurt, plain yogurt, into which you stir bee pollen because you're on a bee pollen kick even though I tell you you're a doctor and you should know better.
 * In "Turnabout Intruder"of Star Trek the Original Series, Kirk, while trapped in his ex-lover's body, tried to convince Spock that he was him. He mentioned certain events where Spock had helped him and urged him to help him again. Subverted when Spock calmly pointed out that those events could be easily read from the captain's logs and reports.
 * It's rather bizarrely subverted in an episode where an insane former Starfleet officer develops the ability to morph into other people, and Spock is presented with two Kirks at the climax. He somehow can't come up with any questions that only Kirk would know, just so the episode can end with a fight scene. Leonard Nimoy himself was quite upset about it.
 * In the critically acclaimed episode of The X Files "Beyond the Sea", the psychic death row inmate (although if his abilities are real or not are made deliberately ambiguous) freaks out Dana Scully a lot by referring to her by a nickname only her recently-deceased father calls her.
 * Also, in the two-part episode "Dreamland", in which Mulder switches bodies with an Area 51 worker. He tries to convince Scully that it's really him by rattling off some of her personal information. She is not impressed.

Scully: Look... Any of that information could have been gathered by anyone.

Mulder (as Morris): Even that yogurt thing? That is so you. That is so Scully. Well, it's good to know you haven't changed. That's somewhat comforting."

"Siroc: If you're the real Captain Duval, tell us something only he would know.
 * A meta-example in Babylon 5: G'Kar has a vision of an angelic being (in the form of his late father) telling him that it's up to him and his fellow Narns to break the cycle of violence between themselves and the Centauri, or both sides will be destroyed. G'Kar asks "Who are you? Where have you been all this time?" The response comes: "I have always been here" -- and that's when the audience realises the angelic being is actually Kosh.
 * In the Law and Order universe, to ascertain if someone is an undercover cop, the other cops ask what the color of the day is. No idea how this actually works.
 * This was also used on NYPD Blue. The "color of the day" refers to a color that undercover officers wear to distinguish themselves from real criminals. If a bunch of cops raid a drug den, they might think twice before getting too rough with someone who's wearing, say, a green shirt if that's the color of the day. If you look at the blackboard behind Sipowicz's desk there's an entry for the color of the day, filled in each morning by Fancy (or whoever). Since NYPD Blue always strove for realism this is probably Truth in Television.
 * Also used on The Chicago Code.
 * 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.
 * In Lois and Clark an identical brush of the hand on her cheek finally (and accidentally) clues Lois Lane in on the fact that her boyfriend isn't just a mild-mannered reporter.
 * In Red Dwarf, Rimmer tries to discourage Lister from going ahead with his plan to become Rimmer's superior officer by posing as Kristine Kochanski (who Lister had a crush on and wants to revive as a hologram). Rimmer succeeds in convincing Lister that there's no point in doing it as "she" has no interest in him at all... until "she" says, "I want a man who's going places. Up, up, up the ziggurat, lickety-split!"
 * When Haley has locked herself in the tutoring center during a school shooting on One Tree Hill, she identifies her husband when he completes their catchphrase through the door ("Always..." "...and forever.") and lets him in.
 * In the Young Blades episode "The Chameleon," after Captain Duval gets himself thrown in jail and the Musketeers believe he is a shapeshifter trying to frame Duval:

Duval: Like what?

D'Artagnan: Like what we got you for your last birthday.

Duval: Nothing. Bunch of thoughtless, shiftless recruits.

Siroc: Yeah, that's the Captain."


 * In the Community episode "Conspiracy Theories and Interior Design" Jeff recognises that only the Dean could possibly have written Garrity's ridiculous lines.
 * In the The Sarah Jane Adventures episode "The Man Who Never Was", Luke twice sends a message to Rani and Clyde by unconventional means. Both times he proves it's him by calling them "Clani".

Mythology and Religion

 * It's believed that the Japanese custom of answering the phone with "moshimoshi?" was to affirm the speaker as human.
 * Older Than Feudalism: In The Bible, after Jesus comes Back From the Dead, not all of his disciples recognize him right away. On one occasion, he walks and talks with two of them all the way from Jerusalem to Emmaus, and they don't realize who they are talking with until he prays before a meal -- apparently, the prayer was something only he would say. (Then, as soon as they recognize him, he disappears.)

Video Games

 * In Final Fantasy VI, King Edgar takes charge of a band of thieves under the rather transparent anagram "Gerad." Celes claims it can't be anyone but Edgar when he refers to her as "My lady," though the fact that "Gerad's" clothes are just brown versions of Edgar's royal blues didn't exactly help to keep his identity secret either.
 * In Metroid Fusion, Samus (and the player)
 * That line was used again in the trailer for the upcoming game Metroid Other M as a cue to the audience regarding what game Nintendo was announcing.
 * In Metroid Other M itself, Samus recognizes Anthony Higgs when he calls her "Princess" near the start of the game,
 * In Zone of the Enders: Dolores, i, James realizes that the Orbital Frame Dolores is connected with his supposedly dead wife when he hears her singing a lullaby she used to sing to their children.
 * Riku identifies Roxas as Sora's Nobody this way in Kingdom Hearts 358 Days Over 2. After the two have a skirmish, he says "Come on Sora, I thought you were stronger than that." Without thinking, Roxas replies "Get real! Look which one of us is winning!", and immediately wonders why he said it, while Riku realizes that his opponent is "his Nobody".
 * In Digimon World 2, at some point late in the game, a member of the Blood Knights, Commander Damien, disguises himself as a Black Sword cadet. Your character gets suspicious, and in an attempt to draw him out, calls out "Commander Damien, sir!". Damien, of course, responds, but not long before he realizes he just blew his cover.
 * As in the Real Life example above, quarians in Mass Effect are taught a certain phrase to use when returning to the Flotilla, as they usually arrive on a different ship than the one they left on. If they don't provide that phrase when prompted, then the Flotilla knows that they're returning under duress, and their ship is destroyed. They even have a separate phrase that sounds right if you're not in the know, but signals the Flotilla that something is wrong. It's also a strong signifier of the quarian sense of communal duty, since it also means that the ship they are on will be destroyed.
 * Another example occurs when, if you gave Tali the geth data during her personal mission in the first game, you can use it to prove it's really you when you meet her again in the second.
 * Played with in the Dawn of War II: Chaos Rising campaign, in which one of six characters performs a Face Heel Turn depending on their Corruption level. If Tarkus is revealed as the traitor he spends the mission giving his former Battle Brothers advice and quoting the Codex Astartes, which infuriates them, because no traitor is worthy to do such things.

Web Comics

 * In Dominic Deegan: Oracle for Hire, Gregory is disguised as "ace reporter Buzz Beardman"... but Rachel recognizes him right away when she hears the name, because Gregory created Buzz Beardman as a character in a comic book he made as a child.
 * Klo Tark's spirit identifies himself by mentioning "he who I would call my brother", his last words as a living person, to Dominic, the person he was referring to with said last words.
 * In The Order of the Stick 397, Nale identifies himself as the Evil Twin by responding characteristically to an insult directed at his Evil Plans.
 * This same trait is later used in an inversion of this trope: Part of Tarquin's evidence that Elan is not Nale is that Elan did not ramble about his intellectual superiority, which Nale would have done.
 * Bob and George: Don't say "What?" in response to your name if you want to go for Implausible Deniability.
 * In Sluggy Freelance, not so much Something Only They Would Say as Something Only They Would Do. Upon his return, Torg hugs Bun-Bun. This results in the inevitable beating. The other characters know that it's 'their' Torg, as only he would do something so stupid.

Web Original

 * In the Paradise setting, a number of people who have been involuntarily Changed into Funny Animals use this method to convince friends and loved ones that it's "really them".
 * In Red Panda Adventures, when the Flying Squirrel is hypnotized to believe that the enemy they're fighting is the Red Panda and the Red Panda is the bad guy, the Panda proves his identity by whispering "Kit Baxter, behave yourself!" in her ear.

Western Animation
"Charmcaster (as Gwen): Who are you guys going to believe? This liar, or your own eyes?
 * Inverted in X-Men; Morph, Back From the Dead and evil, has taken the form of Wolverine, and Jubilee finds them circling each other. One Wolverine shouts that she should shoot them both, and so naturally she shoots the other Wolverine - the real one. It's even funnier because if she had just blasted both of them, the real Wolverine would have been protected by his Healing Factor.
 * Elisa Maza of Gargoyles identifies her brother when he automatically answers her "cross my heart" with "hope to die", complete with the particular series of gestures the two of them customarily use with the phrase.
 * Again in Gargoyles, when Goliath is kidnapped by a shape shifter. When Elisa comes to save him, the shifter naturally takes her form. Since he and Elisa have been having trust issues the whole episode, Goliath tries to identify the real Eliza by shouting "Tell me the truth! Did you ever doubt me, even for a moment?" when Elisa sweetly replies, "Never!" Goliath knows that's the fake and tells his Minotaur cop-friend to shoot.
 * In Darkwing Duck, NegaDuck once dresses up as Darkwing to fool SHUSH. Then he runs into the real Darkwing in the presence of others, but confuses them by anticipating and copying his reactions and words exactly in real time... until the original suggests there's something cute around, triggering an immediate Axe Crazy Berserk Button reaction from his Evil Twin.
 * Happens twice in Ben 10. When Ben turns into Heatblast for the first time, a horrified Gwen doesn't recognize him and is about to use a fire extinguisher on him when he says 'Don't even think about it, freak'. This is when she realizes it's Ben.
 * The second time is in A Change of Face when Gwen and Charmcaster have exchanged bodies and the real Gwen must convince her family of her identity. The following conversation takes place:

Gwen (as Charmcaster): Ok, if you're Gwen, you should know the name of the teddy bear Ben sleeps with.

Ben: Hey! Furry Freddy has his own bed! It just...happens to be next to mine.

Gwen (as Charmcaster): (facepalming) You just gave her the answer, you dweeb! Did your parents send you to doofus school, or were you born like this?

Ben: (wide-eyed) Gwen?! It really IS you!"

"Starscream: Who disrupts my coronation?!
 * In the Transformers movie, after Megatron's death, people are suddenly surprised by the arrival of a new, purple-and-black robot who crashes Starscream's coronation. Then he opens his mouth and smugly demeans the Decepticon's new leader before easily killing him.

Galvatron: Coronation, Starscream? This is bad comedy.

Starscream: ...Megatron? Is that you?!

Galvatron: Here's a hint! (Transforms into a laser cannon and reduces Starscream to ash)"

"Jade: Hey Jackie, will you take me to Moose World this weekend?
 * Done at least twice in Jackie Chan Adventures. The first time, Jackie is split into an overly nice half and an asshole half, and when asked which is the evil one, Nice-Jackie dissolves into tears and proclaims that he must be the evil one because he just killed a bug. Cue aside glances.
 * The second time played it a little straighter with normal-Jackie fighting an evil clone. The good guys want to help but can't tell them apart. Captain Black asks them when his birthday is, and is dismayed when neither of them know the answer. Jade figures it out pretty quickly.

Clone Jackie: Of course-

Real Jackie: -not. You have homework.

Jade: *disappointed* There's your clone."

"Vanna: Steve! Rusty! It's me, Vanna! You've got to let us in.
 * The entire episode had a lot of this since each member of the J Team had an evil clone. Jade recognized that the Paco they had was a clone when he pronounced her name correctly.
 * A variant of this trope appears in an episode of Goof Troop. Goofy and a double, who is a criminal, are in the same room, which Goofy had been wallpapering. Max identifies his father by leaving an open can of wallpaper glue in the middle of the floor and asking his dad to step forward. Both of them step forward, but only the real Goofy steps in the glue.
 * In the The Legend of Zelda cartoon episode "Doppleganger", Ganon kidnaps Zelda after using a magic mirror to create a dark-clothed evil Zelda clone to replace her. Late in the episode, the real Zelda has freed herself and both versions end up covered in mud to the point where it's impossible to tell them apart. Link proposes a kissing contest to identify the fake. He rates the first Zelda's kiss as "very good," but gets a smack in the face instead of a kiss from the second ("*sigh* That's my Zelda all right.")
 * In the Fairly Oddparents, in the episode "Twistory", George Washington is supplanted by Benedict Arnold in disguise. Timmy discovers who is the true Washington by describing how good the quality of the wood of a coat rack is; the supplanter answers "So what?", but the real George Washington, who is obsessed with chopping anything made of wood, jumps and destroys the poor rack with an axe.
 * In The Spectacular Spider Man, Venom/Eddie calls Peter "bro" to reveal who he really is.
 * In the Garfield and Friends episode "Binky Goes Bad", Garfield reveals the real Binky the Clown by getting a judge to say, "Order in the court!". The real Binky immediately responded with, "What's your order? Hamburgers and fries?", while the impostor stays silent. Garfield comments that the real Binky had never been able to resist a very old joke.
 * In Young Justice, the way little Billy convinces the team (but mostly Wally) that he really is Captain Marvel is by mentioning how he shouldn't have to bring them nachos and pineapple juice to get on their good side all the time.
 * In the episode "Auld Acquaintances", Red Arrow is hiding from  when Aqualad finds him. To make sure he could trust Aqualad, he asks Aqualad "Who broke your heart?" To which Aqualad replies Tula ... and Red Arrow himself, one of Aqualad's best friends, who was currently aiming an arrow at his chest the whole time.
 * Subverted in the Veggie Tales episode "Princess and the Pop Star." Vanna, still dressed as Princess, tries to get her bodyguards to let her backstage:

Steve: Hardy har har.

Rusty: Vanna Banana's inside, little girl. Besides, if you were the real Vanna, you would know our names.

Vanna: But I just called you Steve and Rusty.

Rusty: Right. But I'M Rusty, and HE'S Steve.


 * Wild West Cowboys of Moo Mesa: Marshall Moo Montana got a letter from "Masked Bull" challenging him. He figured it was actually written by Horribull because nobody else called him "Meatball Head"."


 * In the season two finale of My Little Pony Friendship Is Magic, Princess Cadence convinces Twilight Sparkle of her identity by reciting the song she and Twinkle would sing when she foalsat her.

Real Life

 * The entire concept of the shibboleth, a way of identifying someone as an ally as described in the Book of Judges: where captured Ephraimites are betrayed by the fact that they can't pronunce the "sh" phoneme and would say "sibboleth" instead, is based around this. These days, shibboleths are call-and-response; a belligerent in a war will have a certain phrase and counter-phrase. If an approaching battalion gets the phrase wrong, they're the enemy. If the guard gets the counter-phrase wrong, the outpost is under enemy control. Notable examples include:
 * During the invasion of Normandy, the Americans would open with "Flash," counter with "Thunder," and confirm with "Welcome." This hinges on the fact that a German would pronounce it "Velcome," and caused problems for some German paratroopers that defected, as well as some German- and Yiddish-speaking Jews who had fled German rule and joined the US Army.
 * At the same time, in the Pacific Theatre, American forces would shout words with several "l"s, such as "lollopalooza" or "hallelujah", as, again, the Japanese troops wouldn't pronounce it properly.
 * Similarly, the Dutch resistance would use words with a "g" in it, since the Dutch language uses a "hard" G, a sound that Germans (or Belgians, or French, or Englishmen, or Americans) can't make.
 * Only Dutch people from the Northern half ("Above the rivers") pronounce a "hard" G, those from the Southern half ("Below the rivers") actually pronounce a softer G. Which is the cause of one of many "annoyances" and "mockeries" between "Northerners" and "Southerners".
 * And that in a country smaller than New York or Lower Saxony. Hoo boy.
 * The word "Scheviningen"--a district of The Hague, formerly an independent town--was also a favorite for the Dutch Resistance, as Dutch would read the first two letters as an "S" and then a "ch", while Germans would read it as "Sch", pronounced like English "sh". It would also not give as many false positives, as it is unaffected by dialectical variation within Dutch, and non-Germans would betray themselves in other ways.
 * American POWs in Vietnam communicated by tapping Morse code on their cell walls. One would initiate a conversation by tapping the familiar "shave and a haircut" pattern, and the other would finish with "two bits". If the respondent instead repeated "shave and a haircut", it meant he was a Vietnamese agent.
 * English rioters during the Peasants' Revolt went around looking for Flemish weavers to beat up, identifying them by demanding people say "bread and cheese", which the Flemings did with a distinctive accent.
 * Funny that, since the Flemish actually did that before the English (some 80 years before the Peasant's revolt). They used "Schild en Vriend" (shield and friend), which the French who they were revolting against could not pronounce, making it Scilt, so the Flemish knew who to butcher.
 * Sectarian fighters in Northern Ireland can supposedly identify whether someone is a Catholic or a Protestant depending on how they pronounce the letter H.
 * And, as a more peaceful example, a lot of Swiss people have a habit of making any and all foreigners say 'Chochichäschtli' (a small kitchen cupboard). Not only is it rather difficult to get all these 'ch' sounds right, even if people do, they usually have trouble pronouncing the vowels the correct way. However, if someone is Welsh or Scottish, they usually manage pretty well.
 * FBI turncoat Robert Hanssen was caught this way. After several US agents had been captured and executed by the Soviets, the Bureau knew they had a mole on their hands. No one suspected Hanssen, however; he was even tasked with finding the leaks for a time. Eventually a communique between Hanssen and his handlers was intercepted, but there was no way to tell who the mole was--until an agent recognized a racial slur the mole made as something only Hanssen would say.
 * Former dictator of the Dominican Republic Rafael Trujillo decided that he didn't want any Haitians in his country (the Dominican Republic and Haiti share the island of Hispaniola). So, he had his agents show parsley to people near the border and ask them what it was. The Spanish speaking Dominicans would be able to pronounce the Spanish word 'perejil' ('parsley') properly, while French speaking Haitians would not. Those who couldn't were usually killed and it's estimated that there were between 20,000 and 30,000 deaths in the "Parsley Massacre".