A fireman is at the station house working outside on the fire truck when he notices little Johnny next door. Little Johnny is in a little red wagon with little ladders hung off the side. He is wearing a fireman's hat and has the wagon tied to a dog.
The fireman says "Hey little boy. What are you doing?" Little Johnny says "I'm pretending to be a fireman and this is my fire truck!"
The fireman walks over to take a closer look. "Little boy, that sure is a nice fire truck!" the fireman says.
"Thanks mister", says little Johnny.
The fireman looks a little closer and notices little Johnny has tied the dog to the wagon by its testicles. "Son", says the fireman, "I don't want to tell you how to run your fire truck, but if you were to tie that rope around the dog's neck I think you could go faster."
Little Johnny says, "You're probably right mister, but then I wouldn't have a siren!"