Chocolate is the third most common cause of poisoning in dogs. Certain chemicals in chocolate, notably caffeine and theobromine, can cause erratic heartbeat and in large enough doses can kill your pup. While you're getting used to that idea, consider this: the second most common cause of canine poisoning (after rat and mouse poison) is ibuprofen, the well-known pain reliever. Dogs apparently love the smell and taste, so they chew through the bottles, eat the contents, vomit their guts out, and die. ODing on chocolate and Advil might seem nutty to us, but it's pretty serious to the dogs.
(source:
The Straight Dope)
Originally posted by ProudlySingaporean:
not true, my dog stole a whole bar of chocolate and ate it happily...now she's still alive and apparently always hungry leh