Without further ado, here is the second known "good" knock knock joke:
Oh, sorry, I think I let it run on a bit long. Theodore is a friend of theirs. I asked them why they think he would especially like it. Clive said "Because it's very funny." Then he slowed down to make sure I understood. "It is a very funny joke."
"But why in particular Theodore?" I asked.
Doris thought for a minute to understand what I was asking. "Theodore is intensely interested in linguistics." She answered.
So, there you have it. If you run into a one eyed super intelligent alien named Theodore, try out this knock knock joke on him. English majors also enjoy it.