Knock, Knock.
Who's there?
Hatch!
Hatch who?
Bless you, but please cover your mouth next time.

Knock, Knock.
Who's there?
Xavier!
Xavier who?
Xavier breath and open the door!

Knock, Knock.
Who's there?
Yacht!
Yacht who?
Yacht a know me by now!

Knock, Knock.
Who's There?
Heaven!
Heaven who?
Heaven you heard enough of these silly knock-knock jokes?

Knock, Knock.
Who's there?
To!
To who?
To whom.

Knock, Knock.
Who's There?
Howard
Howard who?
Howard I know?

Knock, Knock.
Who's there?
I did up.
I did up who?
AHAHAHA. YOU DID A POO!

Knock, Knock.
Who's there?
Interrupting cow!
Interrupt--
Moo!!!

Knock, Knock.
Who's there?
Thermos!
Thermos who?
Thermos be a better knock-knock joke than this!