I was told that any amount of chocolate can be fatal depending on how your dog reacts to it. A safe bet is best stay clear completely. And if your dog does manage to consume any is to keep a close eye on it and seek vet help if required. I do understand that it is not always owners fault as a neighbour once posted a large bar of dairy milk through our door for our daughter not to realise our spaniel was going to eat the lot wrapper and all. I can home to a very sick dog with the runs to. Luckly he was ok but it just shows how easyily things happen.