NEVER give a dog chocolate. You don't know how many dogs and cats (and other pets) have come in with problems because of chocolate. I've even had to put them to sleep half the time. A dog eating chocolate is like a human drinking a snake's venom. As for the tuna, too much is bad, but you can still give a dog some once in a while. Too much table food for dogs is really bad for them. It can make them really fat, and then they can get diseases such as arthritis from it. But just giving them a little bit every so often is fine.