A father brought his son into the doctor because the boy had a matchbox car shoved up his nose. All the while the doctor was trying to remove the car, the father kept saying, "I don't know how he did it."
Finally the doctor managed to remove the little car, and the father and son left.
A few hours later, the father came back with the matchbox shoved up HIS nose. He told the doctor, "Now I know how he did it!"