Keep in mind that certain messages just have to do with how things feel in your tummy. Just because something has an unpleasant taste or gives an unpleasant sensation doesn't mean it's bad for you (medicine, anyone?). So don't just look at the message, but at the effects (vomiting, "Poisoned", "Sick"). You are correct about kobolds and rabid dogs making you sick, of course. And about centipedes poisoning you - however, in that last case you might find that eating the corpse of some poisonous animals, while poisoning you, might make it easier for you to withstand poison the next time around (kind of like a vaccine). Watch out for the message displayed sometimes when you eat a giant centipede or a spider. You might find that the effects of poison last a shorter time afterwards. Experiment with monster corpses - as a general rule, "They say if you eat the heart of a dragon you will share in its strength" - i.e. eating certain monsters might make you gain some of their properties. Which is why I advise you to keep eating fire beetles. And keep in mind that goblins, hobgoblins and gnolls might taste awful and go down hard, but they will still keep you satiated in a pinch.
Oh, and do try the giant rat. It's not as bad as regular rat, I promise.
Playing since gamma 10, when necklaces looked like &s. Lithium man. Brass + Lithium. OCG. Illiterate barb. One race and one class to go.