Knock knock. Who's there? Cows go.

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

Knock knock. Who's there? Egg

Egg who? Egg-cuse me, I'm cracking under the pressure to make a good pun.

Knock knock. Who's there? Documentation.

who? This joke is still in beta and the punchline has not been implemented yet. Please try again later.

Knock knock. Who's there? Alpaca.

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