A firefighter is at the station house working outside on the fire truck when he notices a little girl next door. The little girl has in a little red wagon with little ladders hung off the side. She is wearing a firefighter's hat and has the wagon tied to a dog.

The firefighter says, "Hey, little girl, whatcha doing?"
The little girl says, "I'm pretending to be a firefighter, and this is my fire truck!"
The firefighter walks over to take a closer look.
"Little girl, that sure is a nice fire truck!" the firefighter says.
"Thanks, mister," says the little girl.
The firefighter looks a little closer and notices the little girl has tied the wagon to the dog's testicles.
"Little girl," says the firefighter, "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."
The little girl says, "You're probably right, mister, but then I wouldn'thave a siren!"