If you happen upon an abandoned tennis ball while you’re out walking your dog, by chance you may want to refrain from picking it up. You’ll also want to keep your dog as far away from it as possible. Some genius decided it would be a great idea to use tennis balls to make homemade bombs, and police in Washington worry it’s a trend that could make its way around the country. The process itself is considered illegal, and obviously dangerous.

On June 24, 2016 police in Kent, Washington took to Facebook to warn of the trend that normally happens before July 4th festivities. The way to identify these homemade bombs is by the fuse that sticks out of the tennis ball and it could also be wrapped with duct tape. Check out a photo of what it looks like below.

© Kent Police Department

Back in 2000 a dog in Portland reportedly got ahold to one of these explosive tennis balls when his owner found it in the grass and tossed it to him. The ball exploded when the dog bit down on it and he had to be euthanized on the spot, said ABCNews.com.

If you happen upon one of these homemade tennis ball bombs you should call 911 immediately, and warn others to stay away.