The lovechild of Law of Conservation of Detail and Realistic Diction Is Unrealistic, Hesitation Equals Dishonesty is ubiquitous to the point of being unnoticeable. Whether engaging in Blatant Lies or making sure to Let Them Die Happy, any time a character visibly hesitates when relaying information (rather than, say, making an emotional appeal) to another character, it's even money or better that they're being dishonest, and are trying to barely avoid Saying Too Much.
Performance-based works will often use this trope even when the audience knows that the character is lying to avoid a Seamless Spontaneous Lie. If the character tells a lie without any indication of effort, they'll suddenly look like master manipulators, which might be out of character. The trope can also be used on the assumption that Viewers Are Morons. If the character's delivery doesn't scream "lie," the audience might get confused and think that either the character believes what he just said or that his statement is actually true.
The trope extends to videogames, even to the dialogue of the player characters: Even if Statistically Speaking the PC is an excellent liar, there's a good chance the writers will mark his Blatant Lies with the all too subtle "Why, yes.... I AM the assassin you've ordered".
Sadly, belief in this in Real Life makes things even more difficult for those of us who aren't perfect communicators. Fridge Logicshould indicate that the guy with the perfectly-rehearsed story is probably lying his ass off (or is extremely well-spoken, but there's a noticeable difference between the two), rather than the guy who occasionally pauses to collect his thoughts. Subtrope of You Can Always Tell A Liar. Compare Seamless Spontaneous Lie.
This is used in the unaired episode of Kodomo No Jikan. When Reiji asks Rin what she and her friends were doing (making a birthday gift for Aoki), she hesitates a few times when trying to claim they were doing schoolwork. He actually notices it, but either believes her when she says she isn't lying or decides to let it go.
During the Mahora Festival Story Arc of Mahou Sensei Negima!, Haruna flatly asked Yue if she got jealous when the former kissed Negi. When Yue tried to deny that accusation, Haruna noted that she took a fraction of a second too long to answer and that the old Yue would have smacked her for being an idiot immediately. Busted.
In Strikers Sound Stage X of the Lyrical Nanoha franchise, Teana asks Runessa if she has heard of Toredia Graze, and after a surprised pause, she says no. Teana does some more investigation into this as a result of noticing Runessa's reaction, and eventually learns of her past connection with Toredia and eventually arrests her for her role in the Mariage killings, pointing out that the way she responded was what tipped her off.
Mostly inverted in Bakemonogatari. A good rule of thumb in this series is the more straightforward someone seems to be, the bigger the lie they're concealing. Nadeko is hesitant and lacks self-confidence, and her "big secret" is that she likes Araragi (secret only to Araragi, really); on the other hand, Suruga is quite forthright with her sexuality but no so much with her violent hatred towards Araragi for "stealing" Senjogahara from her. As it turns out, her provocative teasing of Araragi is probably a ploy to get Araragi to forget about Senjogahara, even if that means potentially having to seduce him.
Relentlessly used in Silver Age comics, but only when the reader knows it's a lie. A lie that is part of the twist ending (and thus not known as a lie to the reader) will be delivered blithely, while if we know the character is lying, every sentence will begin with "Um...".
In the first issue of The Tick, a man on the street asks Tick if he's the guy who just broke out of the insane asylum (He is). Tick ums and ers for about half a page before coming up with the answer "No."
Draco paused for a moment, weighing, and then opened his mouth - "I see he did," said Harry, and Draco cursed himself, he should've known better, only it had been hard to decide. Later Draco had listened carefully, but he hadn't detected any hesitation or tremor.
Kyon does this in Kyon: Big Damn Hero when Tsuruya asked why he had to return to the clubroom despite he telling her before he was dismissed for the day. It turns out he had to find Mikuru to Time Travel back to the next day.
Kyon: Well, I have to head back in anyway, since ... I forgot my shoes. Yeah. I'll see you tomorrow, alright, Tsuruya-sempai?
In the ending scene of Back to the Future, Marty asks Doc if he and Jennifer become "assholes" in the future and the Doc says they both turn out fine. The sequel establishes the Retcon that Doc was lying to protect Marty from the Awful Truth. In Part II, the refilmed version of that scene (refilmed to accommodate the Jennifer swap) has Doc hesitate before answering Marty's question.
This is actually reversed in Stranger Than Fiction. After a disastrous first meeting, Harold encounters Anna Pascal on the bus, and stumbles his way through an apology, outright stating that he 'ogled' her and it was wrong. She accepts his apology... "But only because [he] stammered."
Averted in Inside Man. When Jodie Foster confronts Christopher Plummer, asking him if it was true that he used to work for the Nazis in WWII, he hesitates for about four seconds...then smiles and says "Yes." Either he was a truly honest man, who was old and had nothing to lose, or he realized that hesitating that long before lying about it would make it obvious that he was lying.
In Murder on the Orient Express, when Poirot mentions to Hector MacQueen the letter naming Daisy Armstrong, the secretary interrupts his own reply. Poirot deduces that MacQueen is involved with the cover-up.
Subverted in The Hollow which involves a group of people trying to cast suspicion on themselves in order to cover for the real murderer. This leads them to try all sorts of tricks to convince Poirot that they're lying when they're telling the truth, and telling the truth when they're lying.
Both played straight and averted in Discworld. While pauses do often hint at lies, several characters, especially Sam Vimes, note that instant responses are even less honest.
A fairly realistic example in The Dresden Files book Ghost Story; Butters and Daniel are impersonating Wardens to try and intimidate a low-level warlock, and it seems to work until he asks them why they don't have the Wardens' trademark swords, at which point Butters hesitates and their cover is blown. However, this example works because Butters was not an experienced liar, he had not had much time to work out the cover story, he was under a lot of stress at the time, and the warlock in question had some form of telepathy and was also exactly the sort of impulsive person who would not stop to consider whether there might be an innocent reason for the hesitation. Ironically, there actually was an innocent explanation for a Warden not carrying a sword ( the person who forged them was trapped in another body that lacked her former magical talent,) but the warlock was too low down in the magical food chain for this information to have reached him yet, and was able to see through the lie when someone who was better informed would not have thought it odd that the imposters had no swords.
From Get Smart: Max's "Would you believe?" segments often included this.
Smallville's Clark Kent is the king of this, pausing for years before delivering a horrible explanation for something that has even the slightest correlation to his being an alien. If you're going to pause that long, Clark, at least come up with a plausible explanation, will ya?
Averted on Lie to Me: characters point out that prepared lies generally cause people to answer more quickly because they have already prepared their story for questioning. The way to catch these people is to ask them to repeat their story backwards: your average liar won't bother to practice enough to get this right, but someone telling the truth will obviously be able to draw on their memory to answer. It's also mentioned, however, that hesitating is a way to make people think you're lying.
In one episode of Monk, Monk's assistant asks him if he saw some embarrassing pictures of her. He hesitates for about a minute (no exaggeration intended), refusing to meet her eyes, before he responds "no". Then, as he walks away, he wretchedly adds, "Yes."
Pick a crime drama, any crime drama... Sometimes seems you can't go two episodes without this trope being the only reason a cop or prosecutor declares someone to be lying, no matter how logical or reasonable what the suspect says is.
Lost's Benjamin Linus falls into the trope rather absurdly. 98% of what he says is at best a half-truth, and after several seasons it's still hard to tell which was which. But whenever he says something the audience already knows is a lie (like, say, that the smoke monster killed Jacob), he hesitates.
KITT: Where are we? Everything is so dark... is it night?
Explained on Friends "The One With the Jam" where Chandler is explaining his problems with Janice which includes him pausing before what could be considered a white lie.
CHANDLER: Okay, well. Janice said 'Hi, do I look fat today?' And I, I looked at her...
ROSS: Whoa, whoa, whoa. You looked at her. You never look. You just answer, it's just a reflex. Do I look fat? Nooo! Is she prettier than I am? Noo! Does size matter?
ROSS: And it works both ways.
Invoked on Frontline, when Brooke edits a pause into the interview of a priest accused of rape to make it look like he's thinking about his answer.
In a season two episode of How I Met Your Mother, Ted is trying to catch Robin out in a lie by asking a string of questions about the wedding she claims that she had. When she hesitates answering a question about the catering, he immediately takes that as his in to accuse her of lying, but she quickly covers by saying that she wasn't sure how to answer the question as there were multiple possible answers. She's got rapid-fire responses for all his other follow-up questions about the ceremony until he gets to "Husband's name?" to which she just stammers in response. It turns out that she is lying and was never married.
Supernatural - after Balthazar rewrites history by un-sinking the Titanic, and is then forced to reset things by a very angry Fate, Castiel and the Winchesters have this exchange. The boys think Balthazar did it because he's a chaotic headcase who hated the Titanic movie, but Castiel knows it was to create fresh souls for his war in heaven.
Castiel:....Yes. (not meeting Dean's eyes) Absolutely. That's what he did.
Inverted in Merlin when Gaius catches Morgana trying to retrieve the mandrake root enchantment that she's hidden under Uther's bed. On asking her if she's looking for something, Morgana doesn't hesitate for a second when she answers "my earring." However, Gaius knows full-well that she's lying, as Merlin has already told him what she's been up to.
According to David Simon this is how the viewers should have been able to tell a certain story D'Angelo tells in the first season of The Wire is not quite true.
On The Middle, Frankie had set up a play date for Brick that went well. Several days passed without the other mother contacting her again, so Sue called her to ask what was up. The other mother said, "My son's been... sick." Sue accepts this, but thinking about it later she wonders why the woman had hesitated, and it turns out she was lying.
The Navy Lark: One episode had Pertwee not only hesitate, but ask Cmdr. Murray to give him a minute to think, before reeling of an improbable explanation. Lampshaded by Phillips as being not too bad given the time he had to come up with it.
Fallout, and doubtless many other older RPGs without much spoken dialog, use this trope to convey to the player that a particular dialog tree choice is... the gospel truth, of course. In modern gaming, tags such as "<Lie>" are included instead to indicate to the player that his character is lying.
The Porre ambassador in the Chrono TriggerFan Sequel Crimson Echoes inserts significant hesitations into EVERY SINGLE ONE of his lines. Him not being on the up and up therefore comes as a tremendous surprise to the player.
In The 1st Degree definitely plays this straight. When you question the defendent Tobin and pin him about the phone message of him threatening Zack, he says "I was trying to...persuade Zack to withdraw the claim." He's lying, you know it and the prosecutor you're playing as knows it.
Parodied/subverted in The Simpsons: Bart's announcement of, "Well, I'm doing a presentation on...fireworks!" is met with his mother saying, "Bart, I wish you wouldn't lie like that" before confiscating said fireworks. Cut to Springfield Elementary, where Skinner is announcing a fireworks show, courtesy of Bart.
Also subverted when Marge asks Homer where he's going, and he replies 'I'm just going outside... to stalk... Lenny and Carl', which is exactly what he was planning to do.
Played straight (And very noticably so) when Homer asks Marge whether she thinks he's smart or not. She hesitates for quite a while before answering 'yes'. He then asks why she waited so long to reply. After a second long pause she answers 'No reason'.
Parodied as well in The Looney Tunes Show, when Daffy accuses Porky of this due to his stutter when trying to get out of paying a littering fine. No one buys it.
Richard Dawkins was asked in an interview if he could "give an example of a genetic mutation or evolutionary process which can be seen to increase the information in the genome" — a question that, he later said, "would only be phrased that way by somebody who doubts that evolution happened." He famously paused for eleven seconds before answering, and the tape was used by creationists to claim that evolutionists don't have all the answers. Dawkins explains he had actually just realized that the documentary being filmed wasn't what he thought it would be, and was trying to decide whether to throw them out or not. His full, non-"soundbite" answer can be read here.
This Cosmo article is doing its best to make the belief more prevalent. Note that it counts both significant hesitation and simply SWALLOWING while having a conversation.
Military recruiters. Hesitate for any reason, and they automatically assume you're a liar.
Ever hesitated to answer a question your mother asked you? She'll automatically assume that the worst answer must be true regardless of the answer you do end up giving.
Police interrogations, similar to the military recruiters example above. Most reasonable people would give you a few moments to ponder the question "where were you last night between 20:00 and 23:00?" as it's information you wouldn't usually keep accurate tabs on unless you knew it would be important later. Unfortunately, the end goal of an interrogation is to coerce a confession - and any detail that pushes things in that direction is to the interrogator's advantage.