"Animal Parts" and "By-products" mean organs and ground-up bones (in order for the term "by-product" to be listed in the ingredient panel, they can NOT contain feet, beaks, and other non-nutritional parts of the animal.) These are a natural source of glucosamine and so forth. Look at the brands that advertise that they don't have "by-products": they have tons of supplements at the bottom of the ingredient list. I think we all know how supplements are not as good as the real source. Also, when a wolf hunts an animal, they go straight for the organs and eat the bones. Don't be fool by advertising. They are, after all, just trying to make money.