Police are sending a warning to dog owners ahead of the Fourth of July holiday.

Owners and their pets are being told to steer clear of tennis balls. That's because some could actually be homemade fireworks called "Tennis Ball Bombs."

Police say people take the insides of fireworks out and place the material in tennis balls, then add a wick and set them off. In 2000 a Portland man spotted one of these "tennis ball bombs" and tossed it to a dog without knowing what was inside. When the dog bit down, the ball exploded. That dog had to be euthanized immediately.

Police say these "tennis ball bombs" also pose a risk to humans because they can explode in your hands.