While I'm horrified I didn't know about this sooner, I'm glad that I know about it now. Dogs love a treat of human food every now and then, but there are some things that they should never have. Most people know to keep chocolate out of their pup's reach, but the list is longer than just that. Grapes, raisins, and macadamia nuts are all hazardous to your dog's health, although the reasons why are unknown. In the case of macadamia nuts, only 2.2 grams of the food is enough to poison a pup. Onion and garlic should never be ingested by canines, either. Both substances could cause harm to their red blood cells. Even something like onion salt or meat marinated in garlic can have an adverse effect.