We play a silly game with the kids in the pool. We'll go by and pinch them (lightly) and then feign ignorance and say "Hmmm, must be the invisible pool sharks!" It's very silly, but it always cracks them up. They like to turn it around on us as well.
Tonight, the kids and I were in the pool. C swam by me underwater and gave me a little pinch. He surfaced a few feet away and said "Mom! I felt a nibble. I think the pool sharks are at it again! Did you get bit?"
It was so funny that he thought it through and carried the joke that far. It couldn't possibly be him since he also was bit! I just love watching their senses of humor develop.