Thanks for the additional information. I really appreciate it.
The toxicity of chocolate is judged by the amount of theobromine in it. Milk chocolate (like the kind in candy bars), contains 60 mg per ounce of theobromine. The toxic dose is one ounce of milk chocolate per pound of body weight. For example one pound of milk chocolate is poisonous to the nervous system of a 20-pound dog. If you figure it all out, it ends up being that it takes 2-3 chocolate bars to be toxic to a 10 pound dog. Obviously your dog didn't get anywhere near that amount of chocolate, so I'm not terribly worried about it.
Of course, it is always better to be safe than sorry, and the safest thing to do is to induce vomiting in your pup. Details on how to make that happen can be found here: http://www.petplace.com/dogs/how-to-induce-vomiting-emesis-in-dogs/page1.aspx
The best thing to do is give him some peroxide. Then adopt a watch and wait posture.. The symptoms of chocolate toxicity include trembling, nervousness, shaking, increased heart rate, panting, and, worse case scenario, seizures or death. Dogs that eat dark baker's chocolate squares are at most risk of seizuring or dying from chocolate. I would also keep an eye open for tense stomach, attempting to vomit or defecate with no success and abdominal swelling as this can be a sign of intestinal blockage from any leftover wrappers that he may have ingested.
I hope this helps!