Knock knock. Who's there? Cows go

Cows go who? No, cows go 'moo'

Knock knock. Who's there? Dew.

Dew who? Dew-n't worry, it's just a drop in.

Knock knock. Who's there? Water.

Water who? Water you waiting for, open the door!

Knock knock. Who's there? Bye.

Bye who? Bye-gone conclusion, I'm leaving!