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]