Boredom Breaker Naturals Gnaw Stone Stack. Boredom Breaker Naturals Gnaw Stone Stack. All animals love to gnaw on hard materials to maintain healthier teeth, so Boredom Breaker have taken two of the popular wellness gnaw stones, encrusted them with carrot and then sandwiched them in equally 'gnawable' wood rings. For an extra stimulating challenge they can be hung from the roof of your pet's home. Especially recommended for Rabbits, Guinea Pigs, Chinchillas and Gerbils.