Knock knock. Who's there? Cows go.

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

Knock knock. Who's there? Hearse.

Hearse who? Hearse a real groaner for ya: I used to be a baker, but I couldn't make enough dough to roll with the big timers!

Knock knock. Who's there? The author.

The author who? The author who's running out of names for these jokes.

Knock knock. Who's there? Alpaca.

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