Knockknock

Knock-knock is a form of short joke or riddle built on a call-and-response sequence. In its standard version, one person says "Knock knock." The other asks "Who's there?" The first supplies a name or word, the other repeats it and adds "X who?" The first delivers a punny punchline that hinges on the word or its homophone. The humor often depends on a play on words and timing rather than elaborate setup or characters.

Origins: The form emerged in the United States in the early to mid-20th century and became a staple of children's humor in books, radio, and later television. Because it requires only voice and timing, it is easy to perform in schools, homes, and informal settings, contributing to its longevity.

Structure and variations: Classic variants use a name or object that sounds like a question, creating a pun when the final line resolves the prompt. Example: "Knock knock." "Who's there?" "Lettuce." "Lettuce who?" "Lettuce in, it's cold out here!" There are longer versions with multiple exchanges and modern updates that reference pop culture or trends.

Reception and use: Knock-knock jokes are widely regarded as simple, accessible humor suitable for children, yet they also appear in adult comedy and memes. They function as oral games that teach timing, rhythm, and wordplay, and remain a recognizable form within informal storytelling and education.