Medical Mystery

A man goes to the doctor for a checkup.

After the examination, the doctor says, "I am concerned. It seems to me that one of your testicles is composed of wood and the other one is composed of steel." The man doesn't believe what he just heard. "That can't be true! That is impossible! I've never had an operation, and by the way, I have two healthy children." The doctor inquires, "Really? Then how old are your children?" The man replies, "Well, Pinocchio is six and Terminator just turned seven."