Knock-knock joke

The knock-knock joke is an audience-participation joke ending with a pun; knock-knock jokes are primarily seen as child's jokes, though there are exceptions.

The scenario is of a person knocking on the front door to a house. The teller of the joke says, "Knock, knock!"; the recipient responds, "Who's there?" The teller gives a name (such as "Noah"), a description (such as "Police"), or something that purports to be a name (such as "Needle"). The other person then responds by asking the caller's surname ("Noah who?" / "Police who?" / "Needle who?"), to which the joke-teller delivers a pun involving the name ("Noah place I can spend the night?" / "Police let me in—it's cold out here!" / "Needle little help with the groceries!").

The formula of the joke is usually followed strictly, though there are cases where it is subverted.