In a DetectiveDrama, any time a piece of dialogue comes along which is off-the-cuff, not followed up and unrelated to everything, you can tell it's going to be very important. If a suspect turns up late and says "Sorry I'm late, my car was stolen yesterday", the alleged car theft will be significant. If the detective remarks that the suspect has a nice keychain and the suspect says "Yeah, it's from my old fraternity", the insignia on the keychain will turn up later to reveal that the suspect and victim were in college together. Basically this happens whenever the writer can't find a neat way of dropping an important clue into an existing conversation.

See also ChekhovsGun.
Related to the LawOfConservationOfDetail

* In ''Film/TheThinMan'', early in the movie the odd watchchain of The Old Professor was pointed out. That same watchchain was later used in an effort to frame the Old Professor by leaving it at the scene of a murder. (But the Professor's alibi was solid -- at that point he had been dead for over a month.)
* In ''Film/StarTrekFirstContact'', Geordi is giving routine orders to the engineering staff, and tells one of them to check the climate control, since it was getting a little warm in the engine room. It turns out that this was a clue that Borg had beamed aboard and were altering the ship, since Borg ships are warmer than Federation ships.
* ''Film/HotFuzz'' almost parodies this trope (like it does with most police movie tropes). Sgt. Angel makes one offhand comment about each of the minor characters before they are murdered that turns out to be the exact reason they were killed. The thing is, ''he had no idea''. He came up with a complicated theory about why they were killed that had nothing to do with those offhand comments, and he found the killers before he was told their motive.
* In ''Film/DieHardWithAVengeance'', there is an offhand reports about thirteen dump trucks being stolen the night before. Later in the film, it is revealed that these trucks are being used by the villains to cart off the gold they have stolen.
* Inverted in the ''Series/{{Firefly}}'' movie ''Film/{{Serenity}}'' when, as the Serenity crew is entering the bar to meet Fango and Minty, the report that the Reavers invaded a nearby planet, and the survivors had locked themselves in the vault the crew had just robbed (as Mal had told them to do), is playing in the background.
* "Bad for glass" in ''Film/{{Chinatown}}''. This statement made by the Chinese gardener makes no sense until [[spoiler: Gittes realizes he's saying [[JapaneseRanguage "bad for grass"]], referring to the salt water pooling up in the garden and allowing Gittes to figure out Cross's land-grabbing scheme.]]
* In ''Film/TheWolfman2010'', Sir John Talbot warns his son not to go out on the full moon, which [[SchmuckBait sets up]] the inevitable werewolf attack. [[spoiler: The Notable part of this is where Sir John tells Lawrence this because Sir John is the werewolf and ([[XanatosSpeedChess at least, initially]]) doesn't want to be responsible for his remaining son's death.]]

* In James Joyce's ''{{Ulysses}}'', a man approaches Leopold Bloom, asking to read the report on the day's horseraces. Bloom, not wanting to be inconvenienced, tells the man to keep it, as he was just going 'to throw it away'. The man walks away, inspired. The winning horse of the day winds up being the horse, Throwaway.
* In ''Literature/InheritanceCycle'''s first book, [[EnsembleDarkhorse Murtagh]] tells [[TheHero Eragon]] his life story. The thing is, Eragon already knows the most important point--that [[spoiler:Morzan is his father]]--so the main point of the scene seems to be to drop enough hints for astute readers to figure out the next book's TwistEnding, that [[spoiler:Selena is his mother]].
* Any time Literature/SherlockHolmes tells a client not to worry about going off-topic, this trope is in play.
** Notably lacking in [[Series/{{Sherlock}} the BBC modernization]], where Sherlock has considerably less patience for the foibles of regular people. An exception to this is the episode based on TheHoundOfTheBaskervilles, where Holmes specifically takes the case only because the witness uses the word 'hound' instead of 'dog'.

* An episode of ''Series/{{CSI}}'' had one character make an offhand comment about the goldfish in the pond on a suspect's property. Turns out they were pirahnas that the killer had fed the body to.
* ''Series/{{Castle}}'' uses this trope regularly, and inverts it almost as frequently. In almost every episode, minor details dismissed very early in the hour come back and provide a conclusive link to the true killer; in a number of episodes, similarly minor details pull the investigation in a different direction.
* This happens early in ''Series/BabylonFive'' episode "Passing Through Gethsemane", twice even. There's a throwaway scene involving a news report about a criminal sentenced to mind-wipe, prompting Garibaldi and Delenn to briefly discuss its merits and flaws. Brother Edward idly mentions the story of Jesus knowing what would happen if he didn't leave Gethsemane, commenting that he doesn't know if he could do the same. later we learn Edward's ''been'' mind-wiped as a sentence, and while seeking forgiveness for his crimes he gets his chance to answer his earlier comment.

[[AC: VideoGames]]
* There would be no ''Franchise/AceAttorney'' without this trope. Most of the contradictions Phoenix/Apollo/Edgeworth catches are off the cuff, seemingly unimportant statements that wind up screwing over the rest of the witness's claims.
* In ''VideoGame/KnightsOfTheOldRepublic'', you can ask Canderous why his people attacked the Republic. He shrugs and say ''"the Sith came to us with an offer,"'' and the rest of the conversation is about how [[ProudWarriorRace Mandalorians]] thrive on seeking out the most risky fights and challenges the galaxy can offer. You have no way of knowing at the time that "the Sith" he is referring to is [[VideoGame/StarWarsTheOldRepublic Sith Emperor Darth Vitae]], that the Sith Empire is in hiding and quietly building for conquest, that said Emperor was playing everyone [[spoiler: including the then-amnesiac-and-unwitting player character]] as pawns and fools, that he would eventually [[spoiler: get the player character from this game and its sequel to waltz right into his trap, render the player character insane through 300 years of MindRape,]] and turn them loose to play right into his OmnicidalManiac plans...