"How can any cat owner not know that cats are obligate carnivores?"

Dogs are omnivorous but of course they can live on meat; most cats never eat anything else and their food is so loaded with protein that it will shorten a dog's life, to say nothing of ours. Cats make their own vitamin C, for example.

A few months ago I gave my torties a can of tuna. The next time I opened a can they came running over; they had only heard the opening sound once and that was several seconds before they had their first tuna. They remembered.