The kids are going through a phase where they're enamored with cheesy jokes. Knock knock jokes, "why did the [blank] cross the road" jokes, etc. (Thanks a lot "Good Laughternoon" on Sid the Science Kid.)
Except sometimes they try to make up their own and they're not very good at it. Claire does okay occasionally, but Scott... [shaking head]
Here is what the jokes are like:
Why did the picture frame cross the road?
Because it was chasing the milk!
M's response to one of these "gems" the other day was:
Why did the porcupine cross the road?
I couldn't have said it better myself.