What's the deal with Jerry Seinfeld? Did you ever notice he seems to start off all of his jokes in one of two ways?

*knock knock* whos there? sir theres been an accident. theres been an accident who?

"Knock knock." "Who's there?" "Doorbell repairman."

Knock knock?? Who's there?? Jehovah Witness. Knock knock?? Knock knock?? Hello?? Knock knock??