Knock knock. Who's there? Dough.

Dough who? Dough-n't worry, I knead to come in.

Knock knock. Who's there? Silence.

Knock knock. Who's there? Bye.

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

Knock knock. Who's there? (Knock knock.)

(Knock knock) who? Oh, for goodness sake, you just started the joke again! This is an endless loop!