Knock knock. Who's there? Cows go

Cows go who? No, cows go 'moo'

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.

Knock knock. Who's there? Who.

Who who? No, YOU'RE asking 'who.' I'm 'Who.'

Knock knock. Who's there? Alpaca.

Alpaca who? Alpaca the suitcase, you load the car!