CHOCOLATE made for human consumption can cause death in dogs. Dogs are sensitive to a class of chemicals called methylxanthines. Caffeine and theobromine are members of that family.
Dogs simply cannot metabolise and excrete methylxanthines as efficiently as humans. The half-life of those compounds in the human body is in the order of two to three hours, in the dog it is more like 18 hours.
In a dog the compounds are taken up by the liver and transmitted via the bile into the intestine. They are then converted back into the original methylxanthines for another circuit through the animal. This repeats a number of times and instead of getting rid of the substances, the dog keeps poisoning itself.
There are many formulations of chocolate with varying amounts of caffeine and theobromine. The lethal dose of sweet milk chocolate for a dog is two oz per kg of bodyweight. For a five kg dog this would be about 280 grams. A lethal dose of milk chocolate for a 25 kg would be about 1.4 kgs.
Dark chocolate is at least 10 times as lethal. A 25 kg dog could die from the methylxanthines in just five ounces.
Symptoms include vomiting, hyperactivity, restlessness, hypersensitivity to touch (a dog will jump when touched), very rapid heartbeat and rapid breathing rate. A loss of control of leg muscles, muscle tremor seizures, general weakness, coma and finally death follow.
In my opinion it would be a tragic mistake to encourage a dog to develop a taste for chocolate. A small dog left alone in a house with a box of chocolates might well follow his nose to the goodies and commit suicide by poisoning.