Dance Line

During the course of the movie, show ect ect... the characters somehow end up being in a crowd with some nice music. Alice wants to dance, and so she does... then pulls Bob. When Bob was being drawn, he pulls Clair. And while doing so, Clair grabs Emely, and so on and so forth, until almost everyone is in the dance.

This is the Dance Line - wherein people who normally weren't dancing earlier dance because they are pulled in, and in doing so pulls another one from the crowd. Singing isn't required, but when it does, it may soon end up with a Crowd Song. Bonus points if Bob or the others cannot dance.

Related to Crowd Song. Usually a form of Happy Dance.

Film - Animated

 * Rapunzel does this upon visiting the Kingdom in Tangled as part of her Falling in Love Montage.
 * Near the end of Happy Feet, the main characters are trying to get all the penguins to dance, over the objections of the elder. They're not forced to dance, per se, but convinced to dance, causing a sort of domino effect.

Film - Live Action

 * In Just Visiting, when Andre and the neighbor maid Amber visit a nightclub, they initiate one which.
 * The title character does this in "Cuban Pete" sequence in The Mask. He pulls a female police officer out of a crowd of cops and starts dancing with her, and soon everyone's dancing in a conga line.
 * Jenna does this in the Thriller sequence in Thirteen Going On Thirty.
 * In The Muppets, the first song in the movie entitled "I Have Everything That I Need" features this as Gary and Melvin sing in their neighborhood.

Literature

 * A very creepy one in Seeker's Mask by PC Hodgell. Most of the priest's college had been in one for days. Not all of the dancing priests are still alive...

Theater

 * In How to Succeed In Business Without Really Trying (at least the 2011 revival with Daniel Radcliffe; other versions may have had different choreography), J. Pierpont Finch pulls executives from their herd to exemplify problems such as mediocrity and incorporates marshals them into a dance for "Brotherhood of Man."

Western Animation
"Mr. Smithers: Well, I've gotta go. There's a line forming behind me."
 * In the Avatar: The Last Airbender episode "The Headband", Aang is trying to teach some Fire Nation kids how to relax and have fun and does this at his secret dance party.
 * In an episode of The Simpsons, Mr. Smithers is sent on vacation, and goes to a gay resort. He calls Mr. Burns to check up on him...and a conga line forms behind him at the payphone, which he proceeds to lead.