Knock knock. Who's there? Cows go.

Cows go who? No, cows go 'moo'.

Knock knock. Who's there? Donut.

Donut who? Donut even think about leaving me out here!

Knock knock. Who's there? Nobody.

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

Knock knock. Who's there? Alpaca.

Alpaca who? Alpaca the suitcase if you open the door!