Ready, set, fetch! The Chuckit! Whistler keeps 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. Gripable 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.