A 4-year old son was eating an apple in the back seat of the car, when he asked, "Daddy, why is my apple turning brown?"

"Because," his dad explained, "after you ate the skin off, the meat of the apple came into contact with the air, which caused it to oxidize, thus changing the molecular structure and turning it into a different color."

There was a long silence. Then the son asked softly, "Daddy, are you talking to me?"