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. TV shows will sometimes make an entire Musical Episode out of this trope. Obviously, Musicals will have these all the way through. Examples of Crowd Song include: