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 knock-knocks jokes, 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 of the knock-knock, 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 of the knock-knock, 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 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 a knock-knock 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 knock-knock 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 knock-knock 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 knock-knocks 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?)