Toe-Tapping Melody

Someone in a fictional work starts playing a tune. In most musicals, people either join in or serve as the background characters. Then you have a song that inspires people to join in, listen, or even clap. You can feel the joy.

Toe-Tapping Melody is one that inspires a nearby audience or individual to follow along, either by joining in to sing, clap, or acknowledge that it's a catchy melody. It may overlap with Ear Worm if the individual cannot get the song out of their hand. Participation or commentary is key to this trope.

How is this different from a Crowd Song or Audience Participation? Because in-universe, the crowd song or participation may not be spontaneous. Or it can be as little as someone singing along.

Note: The Tv Tropes version of this is called Actually Quite Catchy. I don't like this one because it equates the trope with "Actually Pretty Funny". Happy to brainstorm another title as well.

Advertising

 * [In an award-winning anti-smoking ad], several teens go to confront tobacco executives about the hazards of nicotine. The business executive starts a musical number to "Just Focus on the Positive"; the teens can't help but join in with the number, and drag in the various background extras, including paramedics, nurses, and hospital patients. Yes, that includes the dead ones..

Anime and Manga

 * Played to horrifying effect in a Junji Ito one-shot where a musician plays a screaming melody asking someone to leave her alone. Anyone who hears it can't get it out of their head. Some may hum along. A doctor reveals that the melody is a manifestation of the musician's stalker ex-boyfriend, that died by suicide in front of the musician.
 * The youma in a Sailor Moon episode invoked this by using a soundwave that compels anyone who hears it to want to perform.

Film

 * Subverted hilariously during Hoodwinked. When the Wolf, Granny, Twitchy and the Woodcutter witness, Granny comments, "This is terrible!" Wolf agrees because the rhythm and dancing were way off for the musical number.
 * Happens during Lilo and Stitch. During the fight with Stitch in the Pelekai household, Jumbaa turns the record-player on by accident. He starts swaying to the rhythm of "Hound Dog," giving Lilo and Stitch an opportunity to convene in the kitchen.
 * Tangled shows a contrast of this during "I've Got A Dream"; as Flynn watches with bemusement while Rapunzel defuses the bar patrons. She asks them to sing about their dreams, and dances with them. While Flynn needs to be threatened at knifepoint to sing as well, several rats are bobbing along to the music, as a confused Pascal observes.

Literature

 * In the Discworld novel Soul Music, that this happens is a plot point. Music with Rocks In turns Imp into Buddy, a spoiled diva musician that forgets his harp background when he plays a magical guitar from a mysterious shop. Susan notes that the music itself kept him alive past when his hourglass was supposed to shatter..

New Media

 * The Fine Bros. Entertainment "Try Not To Sing Along" challenge features this for its participants. FBE employees, old and young, need to listen to popular songs and are not allowed to sing along, hum, move their lips, clap, or even so much as tap in rhythm to the music. One deleted video showed that Spongebob Squarepants is super-catchy and hard to resist.

Newspaper Comics

 * Mentioned in a one-off gag in Pearls Before Swine. Zebra says that his herd on the savannah has been using musical alarm bells for warnings about predators. When they go off, the herd sings along.

Western Animation

 * In the Avatar: The Last Airbender episode "The Cave of Two Lovers," several wandering nomads treat the Gaang to Sacred Hospitality as they encounter each other, braiding Katara's hair and adorning Aang with flowers. They also sing about a Secret Tunnel nearby that they plan to navigate. Aang and Katara get into the song and bob along, while Sokka is frustrated and wants to move on with their journey. Quite ironically, he learns that the nomads' music leads to the safest way to navigate the tunnels: badger-moles use earthbending to change the tunnels and singing to them convinces them to lead a path outward.
 * Comes up in Justice League Unlimited in the episode "This Little Piggy". Circe turns Wonder Woman into a pig out of spite; while the League goes to find Wonder-Piggy, Batman and Zatanna confront Circe. They convince her to give them an audience when Zatanna smashes her with a piano. For Circe to change Diana back, Batman has to bare his soul in front of an audience, singing "Am I Blue?" to Circe's nightclub patreons. Zatanna admits he has a lovely voice, and Circe reverses the spell just as Wonder-Piggy is about to end up sliced in a slaughterhouse. Diana thanks Batman for saving her; when he claims to not know what she's talking about, Diana walks off humming "Am I Blue?" cheerfully. Batman can't help but smirk.