Knock-Knock with Jacob

I'm not sure how long ago the kids began their love affair with knock-knock jokes. It started with the girls, but recently Jacob has become more and more enthusiastic about this game. Whenever I am driving the kids around town, Jacob will start in on the jokes, and he will keep going back and forth with me until I give up or the girls distract him. The hitch to this, in case you were curious, is that Jacob is only three years old, and he doesn't quite understand the knock-knock concept. A portion of our conversation yesterday (on the way to the pool) went like this:

Jacob: Knock-knock.
Me: Who's there?
J: Dark Me. [His Wii character at home]
M: Dark Me who?
J: Knock-knock.
M: Who's there?
J: Dragon.
M: Dragon who?

J: Knock-knock. 

M: Who's there? 

J: Dragon who fire on girl.

M: Dragon who blew fire on a girl? 

J: Yes. (evil laugh)

M: Well that's not good.

J: Knock-knock. 

M: Who's there? 

J: Dragon.

M: Dragon who?

J: Knock-knock. 

M: Who's there? 

J: Car.

M: Car who?

J: Knock-knock. 

M: Who's there? 

J: Race car.

M: Race car who?

J: Knock-knock. 

M: Who's there? 

J: Car and race car.

M: Car and race car who?

J: Knock-knock. 

M: Who's there? 

J: Dark Me.

M: Dark Me who?

This will go on, nonstop, for several minutes. He makes me laugh and smile, and sometimes wonder about his 'normalcy'... but hey, who determines what is 'normal' after all? And surely telling a decent knock-knock joke isn't a good litmus test anyway.