Knock knock. Who's there? Ken.

Ken who? Ken I come in already? It's cold out here!

Knock knock. Who's there? Fig.

Fig who? Fig-ure it out yourself, I'm busy!

Knock knock. Who's there? Isadore.

Isadore who? Isadore a lock on this door, or is it just glued shut?

Knock knock. Who's there? The sound of one hand clapping.

The sound of one hand clapping who? Exactly! You're not supposed to be able to answer that.