Someone who pointlessly knocks on the door.
Open the door, hand him the cash and take the pizza
You swimming pull
Knock, knock.
Because they don't like random people knocking on their doors
A visit from the university board of ethics.
Knee-deep! Knee-deep! Knee-deep!
That I will open the door
There's none. They both knock on the door, but never goes in!
Because praying for a bug fix is guaranteed to fail.
A-pasta-ate.