A little boy is riding down the street in a little red wagon that is being pulled by a dog with a rope around his testicles. A man sees this and asks the boy what he's doing.
"I'm a fire truck," answers the boy.
"Well you know, son," the man says, "you should tie the rope around the dogs neck instead of his testicles."
The boy looks back up at the man and says, "but then I lose my siren"