Chocolate contains theobromine, an alkaloid that's chemically similar to caffeine. The chemically pure analog of theobromine is used in medicine as a diuretic and heart stimulant. Most people have no problem digesting the naturally occurring theobromine found in chocolate, but it's an entirely different story for dogs. They metabolize theobromine more slowly and can get sick and die from eating too much chocolate. How much is too much? It depends on the type of chocolate — baking chocolate has as much as 10 times as much theobromine as milk chocolate and thousands times more than white chocolate. To be safe it's best to avoid giving dogs the sweet stuff entirely.