There's none. They both knock on the door, but never goes in!
They just have a feel for that kind of thing.
ANSWER: Because he's afraid someone would look through the keyhole.
If you don't know you must lose a lot of mail.
A tire!
Because she had no arms. Knock, knock. Who's there? Not Susie.
Knock on the door.
Someone who knocks on your door for no apparent reason.
Someone knocking at your door for no apparent reason.
Dind Dong
Test tickles