It takes a considerable amount of choclate to make a larger dog ill and at worst, the small amount of milk chocolate in the M&M"s shouldn't cause more than a upset stomach. Dark chocolate, especially baker's choclate, is the worst. It sounds like your pup is doing ok but if you have any worries, if he starts to vomit, do give the vet a call. All our our pups have on one occasion or another, gotten into chocolate and I understand fully the scare you're feeling! Hopefully he's doing fine! Would love to get to know you and your pup! Sandra