When I was a kid, I loved telling jokes.  I had a joke book that I would read all of the time.  I still remember my favorite:

Q: What's green and flies?
A: Super pickle.

Right.  I know.  Not funny at all. 

This year for Christmas I bought Martin his first joke book.  I figured we could read it together and start building his arsenal of good jokes.  The thing I didn't realize until I started reading them to him is that most jokes play on the meaning of words.  Obvious to me now that I think about it, I didn't get it until I started reading them to him.  Every joke brought on a slew of questions.  For example:

Knock knock.
Who's there?
Police.
Police who?
Police don't talk about me when I'm gone.

Not even a very funny joke, but it really loses the tiny trace of humor that it contains once a 3 year-old starts firing away questions.  "The police are at the door?  Why?  Why are the police there?  The police help you, right?  You should always talk to the police when you're lost, right?"

So we put the book away and I answered all his questions.  About every joke.  Then the other day, he introduced a joke of his own:

Knock knock.
Who's there?
It's me Martin.
Martin who?
Martin John Nelson.

And he laughs.  Laughs his head off.  So, even though he doesn't yet understand a good play on words or jokes about funny situations, he definitely has learned the cardinal rule of joke telling - laugh loud when you're done and others will join in, even if your joke makes no sense.