Siren

A fire fighter is working on the engine outside the station when notices a little girl next door in a little red wagon with little ladders hung off the sides and a garden hose tightly coiled in the middle. 

The girl is wearing a fire fighter's helmet. The wagon is being pulled by her dog and her cat. The fire fighter walked over to take a closer look. "That sure is a nice fire truck," the fire fighter says with admiration. 

"Thanks" the girl, says. 

The fire-fighter looks a little closer and notices the girl has tied the wagon to her dog's collar and to the cat's testicles. 

"Little Partner", the fire fighter says, "I don't want to tell you how to run your rig, but if you were to tie that rope around the cat's collar too, I think you could go faster." 

The little girl replies thoughtfully, "You're probably right, but then I wouldn't have a siren.