Although SOME ‘sponges’ (and Doggie Dental chews), if chewed very well, are easily passed through the digestive system.  Some Veterinarians highly discourage their feeding due to several concerns including the possibility of mild dehydration and sometimes even blockages.  Though most dogs chew them up very well and they are super tasty, often being compared to a nutritious McDonlads french fry, these products are of very poor nutrition quality and should be avoided.  Always consider feeding safer and more digestable products like the Terrabone with condition specific functions.  The pictures reflect each ‘sponge’ in its original state and after being ‘hydrated’ in water.  Hydration times vary.