ok, was training mine, and after he uses some poison breaths, he will eat the stew. He will come "fully fed" when tamed (it seems?), and will only eat after casting poison breath. After some research, My understanding is that the stew is used to replenish the pets use of the skill. I used a pet bonding potion, but not sure how you are supposed to begin the normal bonding process without feeding. I would take the pet and attack some low risk mobs, and get it to use the breath a few times, then you can feed it and stable it.