Any time a large group of people need to sing a song in unison, two things are inevitable: One, everyone always knows all the words; two, no one is ever off-key or out of sync. In other words, no matter how spontaneous the moment is supposed to be, they sound like they rehearsed the song.
In the world of storytelling, there are untold legions of men, women and children ready to burst into song at a moments notice, they only need a nice main character or two to inspire them. Lyrics? Got em memorized. Tricky singing pieces? Not a problem. Choreography? Goes off without a hitch. Every single time.
Naturally, this grows directly out of musical theater, where it's understood that all these people aren't REALLY bursting into song—they're merely acting as the Greek Chorus for the lead characters. For that matter, since the actual Chorus in many Greek tragedies speaks for the general public within the play, versions of this are Older Than Feudalism.
TV shows will sometimes make an entire Musical Episode out of this trope. Obviously, Musicals will have these all the way through.
Compare Combined Energy Attack. Often overlaps with Audience Participation Song. Made possible by Spontaneous Choreography. Taken to the extreme, it's because the lead cast Summon Backup Dancers. See also Sound Off where a military group uses a song or chant to keep everybody in time.
Bizarrely, this is edging its way into Truth in Television with the phenomenon known as a "flash mob," where the performers gather at a prearranged time and place and then assemble as if stepping from the crowd, giving the illusion of spontaneity. Here's an example.
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The horror anime Red Garden does this several times.
Nerima Daikon Brothers has a few. Usually either the villains minions, or the NDB's neighbors complaining about all the singing!
Variation: The Japanese movie Swing Girls has a part where the remnants of a jazz band, after splitting up due to many girls not wishing to continue being part of a band, goes out and plays in front of a store. The girls who split up to live a partying life see them and are inspired to rejoin, at which point they go off to sell their expensive clothing and accesories, and use the money to buy musical instruments, at which point they rejoin those who were playing and play perfectly in sync with the others, despite not having practiced at all.
In the 1971 film, "I've Got a Golden Ticket" was originally going to evolve into this, with much of the town celebrating along with Charlie and Grandpa Joe, but the director nixed that as unrealistic. Interestingly, much the same thing happened with "Easy Street" in the movie version of Annie.
In the 2005 film, this is lampshaded when, after the first such tune, the tour group comments "that did look rather rehearsed," not to mention that it's suspicious they knew Augustus Gloop's name and personality. Wonka chalks this up to skilled improvisation. This oddity was not addressed in the book, which makes the dialogue here further lampshading.
The movie Oompa Loompas are hive-minded drones, so of course they can improvise in harmony.
Ferris Bueller's Day Off takes this a step further. Not only does everybody in Chicago sing along to "Twist and Shout", but many of them dance in unison too.
Somewhat justified. It's a well-known song/dance.
This happens in The Blues Brothers, too. During the concert at the end, Curtis manages to get the whole crowd singing along to parts of "Minnie the Moocher". A better example, however, may be the scene in Ray's Music Exchange - true, the crowd doesn't sing along to "Shake your Tailfeather", but they do dance along, with remarkable accuracy and skill, after which everyone cheers. Presumably they were happy to get the take.
"Minnie" is totally justified, as it's a call-and-response song that Cab Calloway (who is playing Curtis) was known for performing the same way "Curtis" does it in the movie, and the audience would faithfully sing along. It's not like "hi de hi de hi de hi" are difficult lyrics, after all. The one time Calloway actually breaks out into something that's hard to follow (something like "zip-dot-deet-doot-diddly-zip-a-deet-dot-diddly-zip-zap-zeet-do-ooohh"), the audience just laughs in response.
Also when Mrs. Murphy (Aretha Franklin) starts singing at her husband, not only do the customers keep time, but the girls at the counter become spontaneous backup singers. After the song ends, they sit down as if nothing had happened.
Not Another Teen Movie spoofs this with all of the main characters and then some, singing a random dramatic montage ending with all of them dancing and posing at the end. Afterwards, they all look awkwardly at each other and walk off, as if it never happened.
It also got a lampshade hanging. One character comments "Funny isn't it? You would never suspect everyone at this school is a professional dancer."
In The Mask, The Mask uses his powers to get the police surrounding him to join in a big, splashy rendition of "Cuban Pete".
Which lead to the SWAT team getting an offer to open in Vegas.
Spider-Man 3 uses this when alien-possessed Peter interrupts MJ's song, and the band plays and sings along with him perfectly.
While a jazz band might reasonably know how to "comp" an accompaniment, the one in the movie is too good not to have been rehearsed.
Enchanted has the "That's How You Know" scene in Central Park. Robert accepts that Giselle sings (he thinks she's a Cloud Cuckoolander), but is completely astonished when the effect proves contagious and an increasingly large number of random people join in. Somehow, this scene manages to play the trope so straight it meets parody coming the other way.
FernGully has a scene like this based on Zach's Walkman being turned on and playing "Land of 1,000 Dances". The faeries are weirded out and disturbed for a second, and then they're wholeheartedly participating.
To be fair, the crowd only joins in for the chorus, which consists entirely of "Nah nah nah nah".
Elf contains a sequence where the Love Interest leads a group of New Yorkers in "Santa Claus Is Coming to Town"; this is slightly justified in that pretty much everyone does know the words to that song, and in that several people are fairly off-key.
Bran Nue Dae has the final number, a reprise of Nothing I Would Rather Be. Every character in the film gets a second in the limelight.
The recent film version of Horton Hears a Who! uses a Crowd Song for its finale, in which every single character spontaneously bursts out into REO Speedwagon's "Can't Fight this Feeling."
This Crowd Song was especially bizarre since the song really has nothing to do with anything that happened in the movie.
Although considering Horton's personality, him randomly bursting into song isn't that big a shocker...
The jilted boyfriends and husbands out for revenge against Leon Phelps in The Ladies Man spontaneously break into an uplifting crowd song... in the form of a camp Broadway musical number with elaborate choreography.
Mildly subverted in Hairspray, as Tracy Turnblad marches down the sidewalk singing "Good Morning, Baltimore" she walks through a group of women who spontaneously choose to follow her, only to be cut off by "the flasher who lives next door."
In Help!!, the entire earth sings the Ode to Joy (in its original German, no less) to save Ringo from a tiger.
Mildly subverted in the luncheon scene in My Best Friend's Wedding, wherein part of the joke is that the stuffy rich folk actually know the words to "I Say a Little Prayer" in the first place. That they know it in perfect multi-part harmony, accompanied by full-on instrumental track, is another story altogether.
Across The Universe features dozens of bystanders singing the "na na na naaaaaa's" during the "Hey Jude" sequence.
Dancer In The Dark by Lars von Trier turns this into a painfully straight lampshade. The protagonist, Selma, is explicitly delusional, having frequent hallucinations of the people around her joining her in choreographed song and dance. The idea is that she keeps imagining life as a Musical, because "In a Musical, nothing bad ever happens." Did I mention that she has the misfortune of living in a Crapsack World? I really shouldn't need to say it, though, seeing as Lars von Trier seems to hold a citizenship in that unfortunate place...
Tank Girl. When Tank Girl forces the Madam to sing Cole Porter's "Let's Do It" in Liquid Silver, everyone in the club knows the words and can sing along.
Happens in Yes Man when Carl is trying to convince a suicidal man to come back from the window ledge. Having just learned guitar due to a 'Yes', he grabs the man's guitar and starts singing "Jumper" by Third Eye Blind. Then the crowd below starts singing. Then the firemen sent to rescue him start singing.
In Clerks II, there is spontaneous dancing in the parking lot of Mooby's to "ABC" by The Jackson 5.
It would be just a little too obvious to say that a good number of Disney films have 'em. But then, they are patterned after Broadway musicals, and it's been long established (ever since sound was added) that cartoons can sing, dance, and play any musical instrument perfectly without practice.
The latter also occurred in Goof Troop: when Goofy and Pete were in a traffic jam, Goofy started to sing to waste time and all the cars followed!
Casablanca has one to La Marseillaise(France's National Anthem) in protest to the Nazis in the bar singing Die Wacht am Rhein. This is extra effective when you keep in mind that the extras were refugees and exiles who fled France due to the Axis Powers taking over.
Played with in Hot Rod, where Rod starts a normal uplifting Crowd Song of "You're the Voice". More and more people join in, their antics becoming increasingly energetic...until it eventually just devolves into an outright riot as people trash the street. The hero and his friends run like hell.
Rod: What the hell?! Was that because of us!?
Dave: I dunno man! It started out super-positive then it just got crazy!
The Hunt For Red October has a scene where, after Captain Ramius announces their "orders" and gives an inspirational speech, crew members spontaneously start singing their national anthem, though a number of them are audibly off key.
In It Happened One Night, passengers on a bus sing the popular song "The Daring Young Man on the Flying Trapeze" together. Unfortunately, when the bus driver joins in, he neglects where he is driving and swerves off the road into the mud.
In the climax of Horton Hears a Who!, the citizens of Whoville do this in a attempt to make enough noise to prove that the flower they live on is not uninhabited like the Arbitrary Skeptic trying to destroy it believes. It works.
Inverted in The Brady Bunch movie. The Bradys are singing and dancing through the local mall while everyone else are looking at them strangely, clearly not hearing the music.
Jack (the 2013 CBC movie) features a reconstructed approach to this trope; rather than the choreographed-looking crowd songs often associated with movies, this movie uses a more plausible kind where groups of people (in this case, Jack's campaign team) sing on a bus, whether it's singing Parachute Club's "Rise Up" earlier on, or a politics-themed parodical version of Home On The Range later on. Neither crowd song is shown in its entirety.
Not an actual occurrence, but in Men at Arms the narration remarks that Carrot is the sort of person that could pull this off.
In the Thieves' Guild Diary, pickpockets get trained how to do this, as it's an essential part of the "image" (the accompanying illustration is clearly of Ron Moody as Fagin in Oliver!)
In the Star Trek novel How Much For Just The Planet by John M Ford, the Direidians break out into crowd songs around the visiting Federation and Klingon diplomatic delegations on several occasions. It turns out that it was all carefully rehearsed and planned out ahead of time, as part of the Direidian "plan C" to prevent either of the two sides from taking over their planet and disrupting their way of life.
In the Doctor Who New Adventures novel Sky Pirates! this is a stress-induced disorder called Rojahama's Song-And-Dance. It only exists in the System, where reality itself runs on Rule of Funny. (And, since the book expertly twists Rule of Funny into Fridge Horror and back, Benny is deeply traumatised at finding herself singing a song about trusting one another against her will.)
The Australian show The Chaser's War On Everything occasionally sends people out into unsuspecting places, and sees how people react when things suddenly turn into a musical.
The legendary Stephen Bochco misfire Cop Rock tried to combine this trope with your standard law-and-order melodrama (ie, a coutroom scene in which the jury rises to sing 'He's guilty, guilty, guilty...'). What? Yes, that really happened...
High School Musical. OH, NO, NO, NO! STICK TO THE STUFF YOU KNOW... Then again, the song isn't overly difficult to learn. Still, there's perfect harmonies and choreography that doesn't miss a beat...
The students at the high school can all apparently autotune their voices on the fly!
Mocked to great effect in Scrubs's musical episode. All the singing and dancing in the elaborate musical numbers is explained as the hallucinations of a patient with a brain aneurysm.
Mocked is such a negative word. More like honored.
The episode "My Philosophy" featured a transplant patient telling J.D. that she hoped her death would be like a big musical number. When she died, J.D.'s imagination provided this with her performing a song accompanied by many of the cast members.
Kamen Rider Den-O simultaneously twists this around into a Crowd Dance and manages to justify it by having it be a result of the dance-happy spirit Ryutaros having the ability to command people, which he typically uses as the Michael Jackson-like ability to make everyone around dance to a hip-hop remix of the show's opening theme.
Series one, "Mutants": We are the mutant race! Don't look at my eyes, don't look at my face!...
Series two, "The Call of the Yeti": Look into our eyes, everything is good, you don't need your friends or family...
Series three, "Party": Bouncy bouncy/Oh such a good time/Bouncy bouncy/Shoes all in a line...
Fame, the TV show, not so much the movie. While somewhat justified in that the characters attend The School for the Performing Arts, they tended to break out into song an dance when not in class.
Most episodes of Fraggle Rock have at least one instance of this. Arguably justified, in that Fraggles are inherently musical creatures (as are nearly all creatures in the Rock, to a lesser degree), and are strongly implied in several episodes to be somewhat telepathic. Crowd songs often involve creatures other than Fraggles.
The premiere episode of Reading Rainbow in 1983 included an example of this: "Check It Out", an elaborate musical number intrduced by the host, Le Var Burton, to a young child, staged at the Milburn Free Public Library in Milburn, NJ.
This was on th 100th episode, so it was kinda a special occasion.
Another (smaller) How I Met Your Mother example: In one episode, Ted explains the gang's presence on someone's front porch by claiming that they're carolers. They look at each other, then Marshall begins to sing "Silent Night." The rest of the gang joins in in perfect harmony.
Glee. Sure, sometimes the implication is that they rehearsed the song to take us through to the big song-and-dance-number we see as a final version. And sometimes it's a Dream Sequence. And they are a reasonably well drilled show choir. But faaaiiirly frequently, this sort of thing happens, particularly when non-Glee-Club characters (like Emma Pilsbury) are involved... It gets a little ridiculous when they can invent a mash-up, with fully choreography, on the spot, and the band can just keep up.
Television commercials will sometimes feature a montage of "real" people (i.e., actors pretending they're not actors) singing the ad campaign's jingle, with the lyric divided up and several different people each singing a fragment. To convince the viewers that these are "real" people, the montage will always include one or two schlubby types (always white, usually overweight) who are tone-deaf and can barely croak out the lyric. However, all black people in the same montage will invariably have trained singing voices with perfect pitch. Madison Avenue can't acknowledge the existence of black people with no musical talent.
Kids in the Hall - Bruce Mc Culloch sings an upbeat number about "The Daves I Know", and all the Daves he knows join him in the last verse.
In a Monty Python's Flying Circus courtroom sketch, the court compliments Inspector Dim (Graham Chapman) on his cleverness, leading him to break into a music hall-style song about being a window cleaner, and the entire court joins in on a verse. The counsel (John Cleese) then takes up another verse about being an engine driver, and everyone just stares at him until he meekly sits down.
Remote Control - When a contestant is thrown "Off the Air" (eliminated), the audience usually sings "Na Na Hey Hey Kiss Him Goodbye", "Hit the Road Jack", or one of a couple other songs as the player is yanked through the wall.
Opera is the genre that codified this trope, and possibly even made it (we don't actually know for sure what Greek plays actually sounded like, and early opera composers acknowledged that). The interesting thing, though, is that all early operas (such as Monteverdi's L'Orfeo) attempt to justify this, by having most of the music sound as speech-like as possible, or by having it sung by characters who possess supernatural powers.
Margaret: But see, they come - Sir Despard and his evil crew! Hide, hide - they are all mad - quite mad!
Rose: What makes you think that?
Margaret: Hush! They sing choruses in public! That's mad enough, I think!
La Vie Boheme from RENT counts as a small-scale crowd song—everyone in the Life Cafe (except for Benny and his three associates) joins in right on cue after Mark's mocking prayer for the death of Bohemia. It's both spontaneous AND an Ear Worm.
A few songs in Urinetown: The Musical count, but none moreso than "Act I Finale", in which the entire band of the poor people, the two local policemen, and the Big Bad and his henchmen all join in a song about the rebellion's goals.
Two songs from Guys and Dolls count: Luck Be A Lady first has Sky Masterson singing about how badly he needs to win this round of craps, and then all the gamblers around him join in apprehensively singing at him to shut up and roll the dice. Sit Down, You're Rockin' the Boat then features a prayer meeting full of missionaries and the aforementioned gamblers singing about the dream that Nicely-Nicely had last night (which is often implied to have been made up on the spot).
The musical Titanic is made up almost exclusively of these, with only two solos and two duets of any appreciable length.
Like the movie it was based on, the King of Swamp Castle in Spamalot is constantly trying to put a stop to these kind of songs, or any kind of singing whatsoever. He ultimately fails of course.
Sondheim averted some of this in Sweeney Todd: The Demon Barber of Fleet Street — there is a great deal of counterpoint in the crowd songs, with individual members singing different things. Most noticeably shows up in "Pirelli's Miracle Elixir" and "God That's Good!" "City on Fire," on the other hand, is perhaps the only straight Crowd Song in the bunch.
This trope is subverted during a song in the musical How to Succeed in Business Without Really Trying. To get ahead at the office, Finch learns that his boss is a graduate of Old Ivy, and then Finch falsely claims to be an alumnus of that same college. When the boss starts singing the college song "Grand Old Ivy", Finch joins in ... but, rather than singing in unison, he lags slightly behind the boss so that the audience will understand that Finch doesn't actually know the lyric.
1776 gets their Crowd Song out of the way first thing with "Sit Down John". Basically, all of Congress wants John Adams to shut up already.
The "Governer Miller" song in the Takarazuka presentation of Phoenix Wright, done in praise of the titular politician by a gang of reporters.
Do you hear the people sing - both the main song and the reprise at the finale. Being epicified by a 250 persons choir certainly helps.
Elite Beat Agents: This is largely the point of the game, with musical numbers breaking out to inspire people in need of assistance from the titular secret agency.
The main characters of Squaresoft's Final Fantasy X at one point placate the Big Bad by having every person on the planet sing a soothing hymn. The net effect of this effort is a hauntingly beautiful song, suggesting that the United Choir of Spira had been practicing for such an occurrence for years.
Well, they had been. It helps that they had eight or ten psychics acting as mental cue cards.
Lisa(singing): We can't even get any local laws passed without everyone singing, like a big Broadway cast.
Another time Marge was absent during the crowd song which stopped them from being one of their typical angry mobs and asked if they could sing it again. The reply was that it was really one of the spur of the moment type of things, making Sprinfieldians even more impressive than those in the page quote, as they clearly do not rehearse. Good for them.
Marge attempts her own song to prove her point, with limited success.
Oddly enough it was established in a musical clip show that the whole song was video recorded, so if Marge had the song recorded on tape, why did she ask the crowd to sing it again instead of play the tape for her?
Also subverted in an episode where Grandpa bursts in with a line of song after the song has ended. Homer tells him off as he bemoans the fact that he had to take three buses to get to the scene.
Lamp Shade Hanging: My Life As A Teenage Robot and Rocko's Modern Life have featured characters wondering how everybody in a crowd scene happens to know all the words to a song. In the latter, Rocko's the only one who doesn't know them because he never showed up to rehearsals, as shown in the quote at the top of the page.
In the Futurama episode "The Devil's Hands are Idle Playthings", the audience gets in on the action when the Robot Devil interrupts Fry's holophoner opera, including Dr. Zoidberg and Professor Farnsworth:
Prof. Farnsworth: I can't believe the Devil is so unforgiving!
Dr. Zoidberg: I can't believe everybody's just ad-libbing!
In an episode of Family Guy, Peter becomes a receiver for the New England Patriots, and guest star/quarterback Tom Brady warns him not to showboat. So, after he scores a touchdown, Peter leads the crowd, cheerleaders, band, and other players in a full musical number — "Shipoopi" from The Music Man — over two whole minutes, the punchline being that it was just as random in the original play.
There was that dance sequence Peter and friends did at a roller rink.
"I can't believe we did all that! That was totally an accident!"
"The spirit of Massachusetts is the spirit of America/The spirit of what's old and what's new/The spirit of Massachusetts is the spirit of America/The spirit of the red, white and blue"
A small-scale example: The Griffins are on a road trip and Peter decides that they need some driving music and sings the first line of "The Rose." The rest of the family joins in, singing in perfect harmony.
Subverted in Mission Hill, where everyone bursts into song with "Everybody Hurts," but not on key.
And justified, since not only was the song played earlier that episode, but it started off as one person singing it with everyone around joining in after a line or two.
"Smile, Smile, Smile" from "A Friend In Deed" has a large cast of background ponies involved by the end.
A very good case can be made for this particular song happening entirely in Pinkie's mind.
"Small Ass Town (Big Ass Hearts)" from The Cleveland Show, episode, "The Blue, The Gray and the Brown".
The song "Hula-Baloo" from the ChalkZone episode, "Pop Goes the Balloon" might also qualify as a Crowd Song, as Rudy, Penny, Snap, and a bunch of cupid-like characters sing it along with chalk images of teen versions of Rudy's parents to repair their balloon of romance (read: their love for one another) just in time for their second honeymoon to Hawaii.
An American Tail had "There Are No Cats in America", where a random character would sing a verse about a tale of woe from the old country involving cats, and then all the mice on the ship to America would sing the chorus.
The sequel had a similar crowd song called "Way Out West".
On Total Drama World Tour, the very first episode the host Chris outright states the songs will not be rehearsed and will come without warning. However, they all do a very good job of guessing what everyone else is singing, though it's averted twice with Ezekiel and Owen not thinking of a rhyme/interrupting the song to start a new verse.
There was an episode of Pepper Ann made up almost entirely of these...
"I've Got a Dream" from Tangled combines this with an "I Want" Song, as the thugs at the Snuggly Duckling show off their Hidden Depths and share their dreams with Rapunzel and Flynn.
Duckman is peppered with musicals but they are usually duets, no crowd. One exception is "My Feral Lady". The crowds all start singing a lullaby.
Duckman: How come everyone knows this song except me?
Tiny Toon Adventures made liberal use of this trope; even its own theme song was something of a crowd song ensemble performed by much of the cast!
"(Na Na, Na Na Na Na, Hey Hey) Goodbye" to add salt to the wound of a wrestler just fired or announcing he's quitting in the ring.
One of the funniest examples of this was during the Raw after WrestleMania 29. Fans began singing the entrance music of Fandango. However the song has no lyrics and is completely instrumental, so they just sang the melody.
Recently, R Truth has taken this to the next level, as he makes his entrance through the audience and encourages them to sing along to his entrance song, What's Up?.
During the Eric Young, Johnny Devine match at TNA's Hard Justice 2006 PPV, the crowd began chanting "The Roof Is on Fire" for no apparent reason. It turns out the roof of the Impact Zone was actually on fire but the announcers tried to ignore it until the smoke became so bad that they could no longer hide it, but by then the crowed chant had changed to John Cena's catchphrase, "You Can't See Me", which TNA probably hated more than the roof being on fire.
University fight songs are frequently subject to this among raucous NCAA crowds. Sometimes, crowds will even sing along to sufficiently well-known popular music played by the bands.
It's also not uncommon for fans of professional teams that have relatively well-known team songs (e.g. the Philadelphia Eagles) to break out into song anywhere there's a large crowd (e.g. other public events, other sporting events in the city, especially if the Philly team is losing, in theaters...)
For some reason, American college kids feel the need to join into "Sweet Caroline" whenever they hear it. Apparently actual circumstances don't matter, good times have been so good.
"Sweet Caroline," specifically, is a crowd song of the Boston Red Sox and is played at every game at Fenway Park in the middle of the eighth inning. It's popular with a lot of teams, though, including college teams. "Dirty Water" has the same effect on Red Sox fans/the Boston area in general.
Fly Eagles Fly.....
BYU football fans have a crowd song and dance in one with "Popcorn Popping on the Apricot Tree."
Several Youtube videos ("Reach!" and "Reading on a Dream") toy with this idea, showing pranks in which several college students burst into song and dance in, respectively, a college lecture and a library.
Most British Football clubs have their team anthem, hearing 10,000 Liverpool fans spontaneously singing "You'll never walk alone" is quite moving.
Probably more so than the football chant/taunt, "Who ate all the pies? Who ate all the pies? You fat bastard, you fat bastard, you ate all the pies!"
20,000 East London-accented voices singing "I'm Forever Blowing Bubbles"- the anthem of West Ham United, is impressive and interesting in idea too, when you think about stereotypes of British Accents.
When Liverpool face Scottish club Celtic, who also sing You'll Never Walk Alone, the results are something spectacular. Another honorable mention to Celtic during their match against Barcelona. Just don't try to start a debate on who done it first/does it better.
Improv Everywhere once had a bunch of random characters break into song during busy hours in a food court.
A recent advert - T-Mobile Dance - had a huge bunch of people launch into a choreographed song and dance number in Liverpool Street Station in London, with baffled and amused commuters looking on.
Another decent demonstration of this trope in action at a concert is this video from one of Barenaked Ladies' live shows of their song "If I had $1,000,000" which always results in a Crowd Song sing-a-long. If the audience doesn't follow the directions during the last verse, the band will make them do it again to get it right.
The Irish pub, The Wild Rover.
Let's do the Time Warp again!
In fact, any song with their own specific dance (Y.M.C.A., The Macarena, Thriller, The Chicken Dance, etc.). Play it in a crowded area, and watch them dance.
In Japan or at Anime conventions, you can get the same effect with arguably greater enthusiasm with Hare Hare Yukainote That's the Suzumiya Haruhi ED for the 1st season, the Lucky Star OP *
Similarly, "Still Alive" is pretty much guaranteed to have this effect if there is any number of gamers nearby.
Whenever any band dares to play the distinctive opening chord to The Beatles song "A Hard Day's Night" in front of a crowd of Beatles fans, the fans have been known to sing the entire song in response while the band stands there silently.
Debout, les damnťs de la terre. Debout, les forÁats de la faim...
The original YouTube video may have been pulled, but there's nothing stopping them from a more old fashioned Rick Roll.
The Last Night of the Proms. Hearing 40,000 people all sing 'Land of Hope and Glory' in unison is wonderful.
"Bohemian Rhapsody". If the beginning is too slow for some people, just wait. When it gets to "I see a little silhouette of a man," everyone in the nearest vicinity will join in. This has been proven in the car, on camping trips, and while listening to the radio both around the house and while cleaning up a theater.
The same can be said of "We Will Rock You". * stomp stomp CLAP! stomp stomp CLAP! stomp stomp CLAP!*
"We Are The Champions." When it comes to Arena Rock, Queen are the Crowd Song champions, my friend.
Four words: We Are The World. The song was cleverly arranged as a crowd song, the crowd being composed of pop singers in both 1985 and 2010 versions...and many attendees at Michael Jackson's funeral in 2009.
This video. It starts out as a flash mob, but you can see random members of the public joining in. Granted not as well, but still....
Start singing La Vie Boheme in a college setting. You'll have people rocking out in no time.
There are accounts that British sailors, waiting to be rescued while their ships were sinking in the Falklands War, started spontaneously singing Monty Python's "Always Look On The Bright Side Of Life".
Ditto that after the news got out that Sydney would host the 2000 Summer Olympics; the crowd gathered in Manchester decided to console themselves with it.
Gather Scotsmen and alcohol in any one place, particularly if it's actually outwith Scotland itself, and Flower of Scotland tends to fulfill this trope to a tee.
Also any of the classic Burns' songs tends to have this effect also.
This. Somehow even more impressive for not having video.
Caramelldansen can easily end up like this at an anime convention.
A somewhat ironic example: The Offspring's song "Smash". Hearing several thousand people singing "I'm not a trendy asshole/ I do what I want/ I do what I feel like" in unison is... interesting.
In Metallica's S&M, there are several segments of Master of Puppets where the only singing is coming from the crowd.
"Bro Hymn" by Pennywise is utilized in the stadiums for both of San Diego's major sports teams; the chorus is "woah-oh-oh-oh, woah-oh, oh-oh-oh", which sounds oddly stirring with sixty thousand people behind it.
Watch a video of the Hold Steady performing "Stay Positive" and odds are the audience will join in in the "WOAH-OH-OH, WOAH-OH-OH!" part of the chorus
If you walk into a Hofbršuhaus anywhere in the world, even non-German-speaking countries, everyone will join in a round of Ein Prosit (A Toast) any time someone starts it. More to the point, everyone quickly learns Das Hofbršuhaus Lied (The Hofbršuhaus Song) if they spend more than a few minutes there since it's played quite often (every hour on the hour after 5 PM on Fridays and Saturdays at my local Hofbršuhaus).
"Some people call me a space cowboy."
Post the first line of a song on Tumblr, and watch the other bloggers join in on the fun.
Approach any group of girls under the age of 30 and sing the line "Look at this stuff, isn't it neat". They will immediately start singing the rest of "Part Of Your World". This also works for "A Whole New World" most of the time.
"The Devil went down to Georgia, he was looking for a soul to steal."
This. Sort of. Organized, but it wouldn't surprise me if any of the bystanders felt compelled to join in.
No choreography or dancing involved, since the crowd at the time was so packed tight like sardines it might as well have been a mosh pit, but at San Francisco's Fisherman's Wharf after the 2012 Fourth of July fireworks show, the dance show DJ put Katy Perry's "Firework" on the loudspeakers. Cue the whole crowd joining in on the chorus.
There's a very distinctive arpeggio at the beginning of the Animals' "House of the Rising Sun". Cue everyone over the age of 45 or so belting out "There is ... a house ... in New Orleans ... THEY CALL THE RIIISING SUN", while the younger folk look on with a bemused expression. It usually falls apart pretty quickly after that, but everyone old enough to remember Apollo 11 knows the opening lyrics.