Your canine companion will love you even more if you bring home The Whistler by Chuckit! It comes in small, medium, and large to fit everything the need of all dogs from Chihuahua’s to Irish Wolfhounds. The Whistler is also compatible with the corresponding Chuckit! Ball Launchers. To stimulate Lassie’s interest, holes in the ball make a whistling sound as air passes through it.