Why does he have feet?

The other day I went over to my girlfriend's house for a playdate. Her son and T are about the same age. When I got there, I made some joke about Little Bit not having legs yet. Then we chatted as the kids played. About 15 minutes later her son came up to me, pointed to Little Bit's feet and said "He has feet!" "Yes, he does," I said. "Why does he have feet?" he asked. "What do you mean?" I replied. "If he doesn't have legs, how can he have feet?" Then I got to explain to a 3 year old that I was making a joke.