Knock knock. Who's there? A pause.

A pause who? No, just a pause. The joke's over.

Knock knock. Who's there? Next question.

Next question who? Next question... oh, this isn't an interview!

Knock knock. Who's there? Nobody.

Nobody who? Exactly. Why are you talking to the door?

Knock knock. Who's there? Existential Crisis.

Existential Crisis who? I'm not sure, I've been questioning the meaning of my own existence and the nature of identity, so the concept of a 'who' is somewhat fluid to me.