Once a character starts to laugh, all those around him start to laugh as well.

TruthInTelevision, but useful in fiction for getting a group some release from tension. Also, when [[HumiliationConga a proud character is humiliated]], this lets the crowd join together against him.

A character who does not join in is separate in some way -- this may be good, because the humor is unsuitable, or bad, because he's too proud to see the humor. It can result in an attempt to fake it.

Drives the EverybodyLaughsEnding. When a villain doesn't recieve this, it results in a LaughWithMe moment.

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!!Examples
[[foldercontrol]]

[[folder: Anime and Manga ]]

* [[RurouniKenshin Hajime Saito]] does this in his fight against Usui after deducing that the later [[spoiler:BecomingTheMask has become complacent regarding his vendetta against Shishio]]. Of course, after laughing together like madmen, [[HaHaHaNo Usui tells him to shut up]], stating that it's not even funny.
* In ''MyNeighborTotoro'', once the father starts to laugh, the children are able to join in.
* Happens in Part 3 of ''Manga/JoJosBizarreAdventure''. When minor villain Hol Horse warns Polnareff that his sword (Or rather Stand, Silver Chariot) can't beat Hol's gun (Emperor), Polnareff twists that into a fairly crass joke ("What's that? I can beat your bum? Oh, you're into THAT stuff!") and laughs to himself...which causes Hol Horse to lose control and laugh along with him.

[[/folder]]

[[folder: Comic Books ]]

* ComicBook/TheKillingJoke has the Joker tell [[ActuallyPrettyFunny a joke]] at the end and start laughing maniacallly. [[NotSoStoic Batman joins in too.]]

[[/folder]]

[[folder: Film ]]

* MaryPoppins: [[http://www.youtube.com/watch?v=c1dkTrNH92Y I love to laugh! Long and loud and clear! It's getting worse every year! The more I laugh, the more I'm filled with glee! The more the glee, the more I'm a merrier me!]]
* In ''Film/WhoFramedRogerRabbit'',
** the weasels will set each other off. Since they are easily amused, it's less likely to spread beyond.
** In the speakeasy, when the man saying he had seen a rabbit feigns that he has {{Harvey}} next to them, all the rest laugh together.
* In ''PiratesOfTheCaribbean: At World's End'', the main characters on the Black Pearl get involved in a MexicanStandoff (Barbosa, Gibbs, Jack, Will, and Elizabeth). After several ''very'' tense seconds of everyone aiming their guns at everyone else, Barbossa starts laughing, and eventually he can't hold his gun up. Everyone joins in, and lowers their guns too.
** And then Barbossa [[MoodWhiplash breaks up the laughter]], and [[CrowningMomentOfFunny everyone instantly resumes their positions in the standoff.]] See the scene [[http://www.youtube.com/watch?v=FS4eo-f8aOg here]].
* ''{{Seven}}'', despite being a ''very'' dark film has a moment where the main characters all think about the absurdity of the "vibrating" home (it's right on top of a subway,) and all break into fits of giggling despite trying to hold it in.
* In ''EvilDead 2'', laughter spreads through inanimate objects in the room until Ash is unable to resist joining in.

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[[folder: Live Action TV ]]

* In ''Series/{{Mash}}'', when Blake talks of what kidders they are, Burns tries to join Hawkeye and Trapper John's laughter.
* Near the end of season 6 of ''Series/BuffyTheVampireSlayer'', Giles has just come back after a long absence. Buffy details all of the crap the cast has gone through since he's been gone. After she's finished, Giles stares at her for a minute...then bursts out laughing. Buffy's confused at first, but eventually can't help but laughing too.
* A memorable segment of ''{{Coupling}}'' had Jeff describe the concept of 'The Giggle Loop' - the compulsion to laugh in inappropriate situations that only intensifies the more you think about how inappropriate it would be. Later on, they all [[TheFunInFuneral go to a funeral...]]

[[/folder]]

[[folder: Web Comics ]]

* In ''{{Sinfest}}'', [[http://www.sinfest.net/archive_page.php?comicID=2644 Squigley, on a trip, lands in Hell and makes a silly joke, and starts to laugh. The damned join in.]]

[[/folder]]

[[folder: Video Games ]]

* In ''SpaceStationSiliconValley'', hyenas use this as an attack.

[[/folder]]

[[folder: Western Animation ]]

* ''TheSimpsons'': Bart mentions that due to TV he has a very poor memory and can't remember even 8 seconds in the past. The rest of the family laugh at him. "No, really, I can't! It's a serious problem." They continue to laugh. After a moment he starts to laugh too; then while still laughing he anxiously asks "What are we all laughing about?"
** In another episode Burns enjoys an EvilLaugh over his latest plan, and Homer (who the Evil Plan will directly affect) joins in the laughing. Then Burns stops but Homer keeps going for a while.
** This also happened between Homer, Patty and Selma, much to the two sisters' immense chagrin.
-->'''Patty:''' Cut him a check and get him the hell outta here!
* In one episode of ''{{Futurama}}'' an EvilLaugh in a haunted house has this effect on Zoidberg.
-->'''[[EvilSoundsDeep Voice]]:''' [[EvilLaugh Bwhahahahahaha...]]
-->'''Leela:''' What's that!?
-->'''Zoidberg:''' I don't know, but it's contagious! Heh heh heh!
* On the ''WesternAnimation/LooneyTunes'' short "Robin Hood Daffy", PorkyPig as Friar Tuck laughs at DaffyDuck's clumsy attempts at being RobinHood. Daffy walks up to confront him, but soon starts laughing as well.
* In the special ''[[DisneyAnimatedCanon Goofy's Success Story]]'', Goofy became an accidental star by laughing in a theater. The onstage gag wasn't funny to anyone else, but his laugh got them going.
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