This is a great question. There are lots of human food items that are not good for dogs. Most would require to be fed in large quantities to have an adverse effect. In most cases the worst symptoms would be temporary diarrhea or muscle spasms, but some (such as chocolate) can have more serious consequences. Foods known to be toxic to dogs include chocolate, onion, garlic, macadamia nuts, green parts of tomato plants, potato peelings, raisins, grapes, rhubarb leaves, yeast dough, hops, coffee grounds/beans, broccoli and pips or stones from many household fruits.