A boy is sitting on a park bench when he sees a ma

A boy is sitting on a park bench when he sees a man with a strangely tiny head walking his way. The boy asks, "Sir, why do you have such a little head?"
The man answers with a story, "One day when I was younger, I was fishing at the end of the dock and I got a huge bite. To my surprise, when I pulled in my catch it was a beautiful mermaid, and she told me she would give me anything I asked for it I let her go free..."