A word of warning chocolate is very toxic to dogs and can be fatal,
DOGS and the CITY | Useful Information | Chocolate Article
Why Chocolate's Dangerous

Cocoa powder contains Theo bromine, a substance that's tolerated by humans but only a fifth of us realise its toxic potential when fed to dogs. Most dogs will vomit and become extremely restless after eating a large portion of chocolate but even small amounts can be lethal.

A dog's metabolism works differently to ours and isn't effective at ridding itself of Theo bromine; the compounds are taken up by the liver and transmitted back into the intestine where they continue on another circuit through the dog. This repeats itself several times so ridding itself of the toxins the dog keeps re-poisoning itself. A certain amount will stay in the dog's system, increasing for every piece he's fed. When you next feed your dog chocolate the Theo bromine residue will increase the likelihood that you'll one day wake up to find Pooch either dead in his basket or suffering seizures as he leaves your side forever.

A Little Can Kill

Just 100 - 150g of rich, dark chocolate, equal to a small bar, is enough to kill a Chihuahua, a toy poodle and other miniature breeds whereas it would generally take around 400g to kill a dog the size of a Labrador, unless the dog is particularly susceptible. Milk chocolate is less toxic but a 250g bar could still kill a small dog.

Small amounts are less likely to be fatal but because of the build-up of toxins in the body, a little fed to even the largest dog on a regular basis will eventually lead to serious problems.