Ready, set, fetch! The Chuckit!® Whistler® keep the game of fetch interesting and challenging for your dog. Four holes in this high-bouncing rubber ball produce a whistle as it soars through the air to keep your dog interested and focused. The grip-able rubber ball is made just the right size to use with your Chuckit! Launcher. These high-bouncing balls are available in sizes small, medium, and large, with one and two-pack options.