Can one piece of chocolate cereal hurt a little dog?

It's not advisable to feed chocolate to dogs, regardless of the amount. Chocolate contains theobromine, a substance that can be toxic to dogs. The amount of theobromine in a piece of chocolate cereal may not be enough to cause serious harm to a small dog, but it's still not a good idea to take the risk. If you're concerned that your dog has eaten chocolate, it's important to contact your veterinarian right away.