Different creatures have the ability to digest different things, that is correct. Bacteria plays a big roll in this! The (prefered) food in the intestines of one creature could kill another (if one were to only look at the digestion aspect and nothing else)! Take termites for instance, they can eat wood! I certainly can not! But humans can eat termites! The termites (and any other specialized feeder) can eat their unique food source because of their intestinal environment (microcosmos) created by their body. This is accomplished by pH balance, digestive enzyme production and secretion (the enzymes are preferential food of the creature specific) and by the kind of bacteria living in the intestines of that specific creature. I do not have the same microcosmos in my intestines as a termite does so I can not eat wood! If I were to eat termites, for the time frame that the digesting termites I ingested travel through my intestines I will have a more complete digestion of other wood like fibers such as what is in asparagus stems. Once the termites and their enzymes leaves my intestinal tract that slight benefit is gone again. The digestion of wood like fibers would still however be more complete, more thorough, in the controlled, sequentially timed intestinal tract brewing recipe of the termites! We, and so also chameleons, benefit in marvelous ways from the things we eat.