Chestnuts are safe and healthy for dog consumption. The problem, however, lies in the buying and prepping method.  Raw chestnuts and store-bought chestnuts are toxic to dogs. Since raw chestnuts contain shells that are hard for dogs to chew, they may swallow them whole resulting in choking. Store-bought chestnuts contain seasoning and flavors which are toxic to dogs. If a dog eats raw chestnuts without gagging, they'll cause stomach or intestinal blockage. That's why it's best to cook, boil or roast the nuts before giving them to dogs. To safely feed your dog raw chestnuts, remove the shell and crush the nuts into tiny pieces to avoid choking.