A man was walking on the sidewalk and noticed up ahead that a
little boy was wearing a red fire man's hat and sitting in a red
wagon. It appeared that the wagon was being pulled slowly by a
large Labrador Retriever.

When he got closer to the lad, he noticed that he had a rope tied
around the dog's testicles, which probably accounted for why the
dog was walking so gingerly.

Smiling, he spoke to the little boy, "That's really a nice fire
engine you have there son, but I'll bet the dog would pull you
faster if you tied that rope around his neck."

"Yeah," the boy replied, "but then I wouldn't have a siren."