Nothing, because he is the one who knocks.
CORNY JOKES!!!
Because if it were invented anywhere else, it'd be called a teethbrush.
And what is the person inside to say "who is it "
Someone who knocks on your door at 6 a.m. for no reason.
Shaking Bad.
I am the one who Knock-knocks.
Two wee chaps
Cuz freedom rings, baby!