Ready, set, Fetch!. Give your dog something to jump for with the Chuckit!® Whistler Ball. Durable rubber ball keeps the game interesting and challenging for your dog. Four holes in this high-bouncing rubber ball produce a whistle as air passes through to keep your dog interested. Grip-able rubber ball is made just the right size to use with your Chuckit!® Large Ball Launcher (Sold Separately).