Keep an eye on him. Chocolate is toxic to dogs, but some dogs will eat an entire bag of kisses and be completely fine, other dogs will eat a tiny bit and start throwing up. He will most likely get sick and throw up, just keep an eye on him and if it seems to get worse or he starts acting funny, take him to the vet You may also want to call a vet now (some have 24hr emergency service) and just ask them what to look for. They should be able to at least tell you something over the phone.