To really consider animal digest you have to understand that animal digest is natural flavour. This definition is found in another article in Wikipedia titled "Natural flavors" which lays out pretty well how this is true. Animal byproducts, bone, mechanically separated tissue, blood, ofal, and the like, from any specie in a world wide context, but limited to domesticated species excluding dogs, cats, pet snakes and the like, euthanized animals of any sort (they are poisonous) any poisoned animals, rats and other vermin, in the Commonwealth, EU, US, and most South American nations. These materials are chemically (Hydrolysis)and enzymatically disassembled to the basic proteins, their salts, esters, flavinoids, and other compounds which can be reassembled to add, improve, enhance the flavours which are already present. Sometimes to make a product like pet food smell nicer to the human serving it though not necessarily more flavourful to the pet. This is a multibillion dollar industry that has to hide its good taste because it seems, as above, "GROSS". J. Barbara Gershom, BSME, MSFS, PhD For more info goto www.fsis.usda/help/faqs  usda