Foods that are toxic to dogs include avocado and bread dough, according to the American Society for the Prevention of Cruelty to Animals. Other foods harmful to dogs include chocolate, grapes, macadamia nuts, onions and garlic.
In general Guatemalan avocados are most toxic to dogs, the ASPCA writes. Raw bread dough is dangerous due to the possibility of its yeast expanding in the dog's stomach. Caffeine and theobromine are the most dangerous elements in chocolate, and darker chocolate is more toxic to dogs than milk or white chocolate. Dogs usually are unable to consume enough raw onions or garlic to cause toxicity, but concentrated forms of onion and garlic, such as garlic powder, are more dangerous. Finally, macadamia nuts can cause weakness in dogs' rear legs, pain, tremors and fever.