3 year old humor

Yesterday Justin and I were home all day together.  I didn't have work because school was only in session until lunch time, so, we were hanging out at home together.  We made chocolate chip cookies, put up some fall decorations, did laundry, etc.

At one point, I was in the laundry room folding clothes and Justin came to find me.  Following is how our conversation went:

Justin:  Mom, I have a joke for you.
Me:  Okay, what is your joke.
Justin:  Knock, Knock.
Me:  Who's there?
Justin:  Justin.
Me:  Justin who?
Justin:  Justin Henry Leader.

At this point in the conversation, he turns around and leaves the room giggling.  I could then hear him say, "That was so funny!" with another giggle.

I'm not sure where he came up with this joke from and I didn't even know that he knew what a joke was.  I know this joke is not funny, but to his 3 year old mind it was very funny.

I wonder what he will come up with today?

Take care,
Michelle