Hollow Design: Allows you to store small kibble or small treats inside the ball. Your dog must nose the ball to roll it and dispense treats. Warning: Chewing the ball will not release the treats. Irritated Surface: Put some of his favorite peanut butter on the surface of the ball. Perfect for puppy teeth and teeth cleaning. Egg Shaped: Unlike regular round balls, the egg shaped rolls irregularly making this a very interactive dog toy .