You Can Always Tell a Liar

A tell is a very subtle, but nonetheless noticeable, change in a person's behavior, appearance, or demeanor. In poker, a skilled player can detect another player's tell, and thus can generally get a clue regarding what the other player thinks of his hand (for good or bad). Similarly, people have unconscious reactions to events around them, things said to them, and other stimuli. Someone skilled in reading body language can use these tells to "read" another person's attitudes, intentions, and sometimes even motivations. Basically, Bob knows that Alice is lying because whenever she lies, her left eye twitches. Her eye twitching is her tell.

Common tells include heart-rate and respiration changes, shaking hands, changes in voice level, sudden and inappropriate displays of confidence or aggression, flushing or blushing, eye ticks, "subtle" glances toward things that the person wants to keep hidden, not meeting the eyes of a questioner, and so on. Some characters have different symptoms.

If a person is unaware that he's giving a tell, this can go on for a while. On the other hand, it is always possible for a person to intentionally fake a tell, and thus lead the observer to make an error themselves. If this goes down multiple layers, with the observer knowing that the subject is faking, it becomes I Know You Know I Know.

Often seen when the characters in a work play poker, naturally, but can appear in other situations.

Pinocchio Nose is the subtrope for tells specifically related to direct lying; please add direct lie-specific example to that page, not here.

A Living Lie Detector can always spot a lie, even if there is no tell. Hesitation Equals Dishonesty is a subtrope.

See also The Tell for characters with a tell that points to their emotional state rather than their honesty.

Anime And Manga

 * In Liar Game, Akiyama instructs one of his teammates about this in the third round of the game. It's a cover for what he's really trying to accomplish, and tells have nothing to do with his actual plan.
 * Also features in the second revival round. Fukunaga apparently betrays Team Akiyama by telling Nao's opponent that she has a tell: she blinks twice whenever she lies. Nao's opponent uses this information to wipe the floor with her...but it's all a ruse, one planned by Nao herself, and as soon as her opponent is feeling overconfident, Nao lures her into a trap that instantly reverses the situation.
 * In Case Closed they bring up a supposed CIA method of lie detection - bringing the target's face uncomfortably close to their own, checking their pulse and iris at the same time.

Comic Books

 * In Daredevil, Matt Murdock uses his superhumanly acute hearing to listen to people's heartbeat, and thus can tell when they are lying. He has been fooled on occasion, though, when the person he's talking to is such a practiced liar that they don't have a reaction to it. And in one case, he was fooled because the liar had a pacemaker.

Film
"Annabelle: How'd you know I was bluffing? I didn't do any of my tells! I didn't shuffle my cards, I didn't pull my hair... I didn't even flick my teeth! Maverick: You held your breath. If you'd been excited, you would have started breathing harder. Annabelle:  I did not. (looks at the Commodore) Did I? (the Commodore nods, and Annabelle looks at Angel) Did I? (Angel nods, and Annabelle looks at the dealer) Did I? (The dealer nods) Well... I'll just pretend I was playing with someone else's money. Maverick:  That shouldn't be too hard."
 * In the 2006 Casino Royale, James Bond observes that Le Chiffre's eye twitches when on a strong hand and deduces that it's his tell. Unfortunately, Le Chiffre was doing it intentionally and waiting for him to rely on it...
 * At the opening poker game in Maverick, Maverick tells people that he's going to lose for one hour. At the end of the hour, he starts winning, and winning big, because he's spend the first hour learning everyone's tells. When Annabelle Bransford gets put out of the final Championship game, the following exchange takes place:


 * The Russian mobster in Rounders played with his cookies when he was bluffing, as the main character noticed mid-game.

Literature

 * Comes up in the Honor Harrington book Flag in Exile. Honor is facing off against  in a sword duel, and the narration goes into detail about tells, which Graysons call the "crease," and how it can be used to predict a swordsman's opponent. It's considered unreliable, since each person has a different "crease," making it difficult to figure out a person's crease without knowing them. Honor is able to instinctively feel  "crease", allowing her to win the fight. Though even she admits she didn't actually know what  actual crease was.
 * In Nineteen Eighty-Four one of the overall goals of those in charge seems to be to make it so anyone can tell when anyone else is lying, without even trying to. More broadly, to involuntarily know everyone else's thoughts.
 * In The Space Merchants by Frederik Pohl and Cyril M. Kornbluth, the protagonist Mitch Courtenay and his estranged wife, Kathy, each know the other's "Tell". This is a hint about how much they know and love each other.
 * In Scratch by Troon McAllister, the prologue is a 32 hour poker game between the main protagonist (Eddie) and the scene's point of view character (Whitman). He picks up Eddie's tell and proceeds to try to kick his ass...but loses horribly. As Eddie leaves the private poker room, the owner asks if he did his usual bullshit tell.

Live Action TV
"Eliot: You have a tell. Hardison: I have a tell? Eliot: Yes. Hardison: I have a tell for Rock Paper Scissors? Eliot: Yes!"
 * Played straight and discussed in an episode of Thirty Rock wherein Jack reveals and exploits the other characters' various tells during a high-stakes game of poker.
 * Once on Mash the guys realized that Winchester whistled louder when he was bluffing in poker.
 * This trope is pretty much the raison d'etre for the TV series Lie to Me.
 * Jack Dalton had a tell on MacGyver.
 * Inverted in Monk: Monk realizes that a suspect who passed a polygraph test was lying when he later told a lie while on a treadmill and didn't show a change in heart rate.
 * Olive in Pushing Daisies answers questions with questions when she's hiding something; Ned has a facial twitch.
 * Played for laughs in one episode of Leverage:


 * In Frasier, Niles' nose bleeds not so much when he's lying as when he's broken his ethical code. Of course, the two overlap.
 * Frasier has one as well: when he's knowingly broken his ethical code, he starts having attacks of nausea.
 * The British panel game Would I Lie to You? has this as part of its gimmick. Savvy guests have tried to block or mask their tells for fear of giving something away (one pulled out a pair of sunglasses; another tried to do several at once).

Radio

 * Fibber McGee and Molly: If somebody's wife always calls him "Fibber" rather than by his given name, you'd be wise to take notice.

Video Games

 * Apollo Justice can tell when a person is lying due to his bracelet tightening in reaction to the tics because Ironically, Apollo's ability is very realistic (not to mention scientifically plausible) in contrast to Phoenix's obviously unrealistic magatama. Trucy has the same ability because , which makes her an excellent poker player.
 * L.A. Noire used high definition and detailed facial software to make it so the players could better guess if the person they are speaking to is lying to them.
 * While early levels obviously have the Mo Capped actors ham it up a bit for the player to get used to the tactic, later in the game the tells become much more subtle and realistic.

Western Animation

 * In Father of the Pride, Sarmoti is the only player in a poker game to know everyone's tells, as well as his own. Every other player seems completely oblivious to their own and each others' tells, or even that this aspect of the game exists. Which is odd because one player's tell is so obvious that everyone immediately picks up on it.

Real Life

 * Microexpressions are an uncontrollable action that lasts just a fraction of a second. Psychologists have managed to connect these to specific emotions, when they don't match up with what a person says they are likely to not be telling the whole truth.