Great concept for an iq toy. The inner ball has two holes one on opposite sides. So you have to cover a hole to fill the top. Then without dropping any treats if you're skilled, you need to move the number ball so that it covers up. The outside has holes all over so not only the dog is in for a skill challenge but also the owner. Often Ill fill it, think I covered the inner holes, roll the toy and everything falls out. Seems like the inner ball should have one hole.