Have you ever drank a lot of coffee on an empty stomach and get a splitting headache? That's the theobromine f*cking you up. I had a vet visit last week, (my dog's got bad allergies) and he like to talk .. a lot.
Chocolate's poison to humans too. It contains theobromine and if enough is consumed it can be deadly. You'd have to have a really slow metabolism and/or eat a sh*tload of it. Dogs metabolize theobromine much slower and can actually consume enough to die.