Joke telling toddler.

We have a knock-knock joke around here that I made up last year for Art's benefit.  The person at the door is Dr. Who.  Dr. Who, who?  "You sound like an owl!" is the punch line and Art loved to tell that joke.  

Well, we've been telling it again lately and Lewis has been listening intently.  Just this morning he managed to get to punch line, even if he did leave out the middle.  He was laying in his crib, talking to himself and I heard him say, "Knock knock! -- Ow-wool!"