Ready, Set, Fetch with the Chuckit! Whistler Ball Dog Fetch Toy. Designed to keep your dog interested, focused and engaged in fetch, these high-bouncing rubber balls have four holes that produce a whistling sound as they soar through the air, giving your dog something to chase after. Made from durable, easy-to-clean rubber, The Whistler is gentle on your dog's mouth as they retrieve the ball. Compatible with Medium Chuckit! Launchers and are available in a variety of sizes for all dog breeds.