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From wiki :
In sufficient amounts, the theobromine found in chocolate is toxic
to animals such as horses, dogs, parrots, small rodents, and cats
(kittens especially) because they are unable to metabolise the
chemical effectively. If they are fed chocolate, the theobromine
will remain in their bloodstream for up to 20 hours, and these
animals may experience epileptic seizures, heart attacks, internal
bleeding, and eventually death. Medical treatment involves inducing
vomiting within two hours of ingestion, or contacting a
veterinarian.
A typical 20-kilogram (40-lb) dog will normally experience great
intestinal distress after eating fewer than 240 grams (8.47 oz) of
dark chocolate, but will not necessarily experience bradycardia or
tachycardia unless it eats at least a half a kilogram (1.1 lb) of
milk chocolate. Dark chocolate has 2 to 5 times more theobromine
and thus is more dangerous to dogs. According to the Merck
Veterinary Manual, approximately 1.3 grams of baker's chocolate per
kilogram of a dog's body weight (0.02 oz/lb) is sufficient to cause
symptoms of toxicity. For example, a typical 25-gram (0.88 oz)
baker's chocolate bar would be enough to bring about symptoms in a
20-kilogram (44 lb) dog. Of course, baking chocolate is rarely
consumed directly due to its unpleasant taste, but other dark
chocolates' canine toxicities may be extrapolated based on this
figure. Large dogs such as St. Bernards or Rottweilers are somewhat
less susceptible to poisoning, but caution is still necessary. As
dogs like the taste of chocolate products as much as humans do, and
are capable of finding and eating quantities much larger than
typical human servings, they should be kept out of their reach.
Treats made from carob are a good substitute and pose no threat.
There are reports that mulch made from cacao bean shells is
dangerous to pets (and other animals).
