A man was telling a story to his four-year-old son. The boy noticed a lock of gray hair on his father's head and asked, "Why is some of your hair gray, Papa?"
"Papa gets a gray hair every time his little boy is naughty," his father replied, hoping to use the opportunity to teach a moral lesson.
The boy thought for a moment, then said naively, "Oh, I see why Grandpapa has so much gray hair. He must have had very naughty boys."