You knock on the door.
The Doors.
The door.
By telling them knock knock jokes!
Someone knocking at your door for no apparent reason.
1, 2, 3, 95, 98, ME, NT, 2000, XP, Vista, 7, 8, 10.
All the extra cubholders.
Swim down and knock on the hatch. (In Sweden we have a running tradition of telling jokes about stupid norwegians. They do the same about swedes)
A: Knock on the hatch.
A submarine
If you open the windows in a submarine, your problems will begin.
A wind tunnel.