JACK'S PROBLEM.
Jack (mystified). "Papa, there's one thing I don't understand kerzactly."
Papa. "Well, what is that?"
Jack. "I dig a hole here on the beach, and a wave comes along and washes over it, and goes back again. Then I find the hole all filled up with sand. I thought the ocean was made of water, but it seems to me it's nothin' but sand."