The following is from the AVMA web site (http://www.avma.org) Pet Owners guide to small animal poisons. Of note are the amounts relative to body weight for poisoning to occur, and the symptoms of poisoning. (Good thing it's not toxic in humans, I'd be long dead by now. Although at the rate given, let's see, I weigh 130 lbs so I'd have to eat 65 ounces (about *4 pounds* :-p) before I'd hit that level.) "It often surprises pet owners to discover that for animals, chocolate is poisonous in sufficient dosages. Specifically it is the drugs in chocolate, theobromine and caffeine (of the drug class methylxanthines), that are toxic to pets. Only a moderate amount needs to be eaten by an animal, typically a dog, in order to be poisonous (approx. 1/2 oz. of baking chocolate per pound of body weight and less in some animals). With the poison in this case being so appealing, overdose is not a rare occurrence. Poisonings of this type typically occur during the holiday seasons of Easter, Christmas and Halloween. Depending on their appetite and the specific ingredients contained in the recipe, some dogs have ingested a toxic dose of chocolate by eating an entire pan of brownies or another chocolate dessert, particularly one containing baking chocolate. Fortunately, the animal frequently vomits soon after which reduces the amount of poison in the stomach available to act on the body and decreases the toxicity somewhat. If clinical signs are seen, these can include vomiting, excessive urination, hyperactivity, fast breathing, weakness and seizures. While rare, death can occur, usually due to the adverse action of methylxanthines on the heart." -Ilena Ayala [Posted in FML issue 2330]