Unlike many jokes that are monologues told with care by the jokester, knock-knock jokes engage the jokester and the audience in a dialogue. There are many different jokes of this type, but there are some shared characteristics.
Formula. All knock-knock jokes have five lines. The first two lines are always the same:
Jokester: Knock-knock. Audience: Who's there?
This exchange is followed by another pair of lines. In the third line, the jokester gives a partial answer which is a real English word and generally makes some sense. In the fourth line, the audience repeats the answer of the third line and adds the question, "who?" like this:
Jokester: Sam and Janet. Audience: Sam and Janet who?
In the final line, the jokester almost always makes a pun on the answer in the third line by adding a subsequent word or phrase that transforms the meaning because it sounds like something else. The closing line to the knock-knock joke we're using as an example is:
Jokester: Sam and Janet evening.
Said quickly, the name of the couple is transformed aurally into the name of a song from the musical South Pacific: "Some Enchanted Evening." Some jokesters actually sing the last line, using the appropriate melody.
Variations on the knock-knock. There are also self-reflective knock-knocks that make fun of the audience's expectations for how the joke will work, like this one:
Knock-knock. Who's there? Banana. Banana who? Knock-knock Who's there? Banana. Banana who? Knock-knock Who's there? Banana. Banana who? Orange you glad I didn't say "banana" again? (Aren't you glad ...)
Here, instead of using the word "banana" in a punning way in the punchline, the jokester uses the name of another fruit. This type of joke works by breaking the formula, while still using the pun concept. Sometimes, the word "who" of the question is incorporated into the knock-knock's punchline, to create a variation like this:
Knock-knock. Who's there? Boo. Boo who? Oh, don't cry!
Another variation is the series knock-knock, in which a set of jokes is told in sequence to create an effect. One set goes like this:
Knock-knock. Who's there? Ann. Ann who? Ann Easter bunny. (An Easter bunny.) Knock-knock. Who's there? Anna. Anna who? Anna other Easter bunny. (Another Easter bunny.) Knock-knock. Who's there? Maura. Maura who? Maura Easter bunnies. (More Easter bunnies.) Knock-knock. Who's there? Howie. Howie who? Howie gonna get rid of all these Easter bunnies? (How're we gonna get rid of all these Easter bunnies?)