Will walnuts make a dog vomit?

Yes.

Their biggest risk is that they can block the digestive system, requiring surgery to fix, but can also be toxic to some dogs and even cause neurological damage. It can also give them cavities.

Also, if the dog is small, it can be extremely harmful, often making the dog very sick. Small dogs could choke or suffocate, and the large nut could griend their teeth and make them more likely to fall out. Peanuts are also bad for dogs, if not in very small amounts.