Knock knock. Who's there? Sew

Sew who? Sew glad you asked, it's a tailor-made joke!

Knock knock. Who's there? That's what I'm asking.

That's what I'm asking who? That's what I'm asking who wants to know who's on the other side of this door!

Knock knock. Who's there? Cows go

Cows go who? No, cows go 'moo'

Knock knock. Who's there? Alpaca.

Alpaca who? Alpaca the suitcase, we're going on vacation!