Avocados contain a substance called persin. It's harmless for humans who aren't allergic, but large amounts might be toxic to dogs. If you happen to be growing avocados at home, keep your dog away from the plants. Persin is in the leaves, seed, and bark, as well as in the fruit.

Beer, liquor, wine, foods containing alcohol, none of it's good for your dog. That's because alcohol has the same effect on a dog's liver and brain that it has on humans but it takes far less to do its damage in dogs.

Onions and garlic in all forms (powdered, raw, cooked, or dehydrated) can destroy a dog's red blood cells leading to anemia.

Caffeine in large enough quantities can be fatal for a dog and there is no antidote.

Grapes and raisins can cause kidney failure in dogs, even just a small amount can make a dog ill.

Milk and milk-based products can cause diarrhea and other digestive upset as well as set up food allergies (symptoms of food allergies can be itchiness).

Macadamia nuts or foods containing macadamia nuts can be fatal. As few as six raw or roasted macadamia nuts can make a dog ill.

Candy, gum, toothpaste, baked goods, and some diet foods are sweetened with xylitol. Xylitol can cause an increase in the insulin circulating through your dog's body and that can cause your dog's blood sugar to drop and can also cause liver failure.

Chocolate contains a toxic agent, theobromine, for dogs. It's in all kinds of chocolate, including white chocolate. The most dangerous kinds of chocolate for dogs is dark chocolate, chocolate mulch, and unsweetened baking chocolate. Chocolate, even a little, can cause a dog to vomit, have diarrhea, and be excessively thirsty. It can also cause abnormal heart rhythm, tremors, seizures, and death.

Fat trimmed from meat, both cooked and uncooked, can cause pancreatitis in dogs.

The seeds from persimmons can cause inflammation of the small intestine in dogs. They can also cause intestinal obstruction.

Peach and plum pits contain cyanide, which is poisonous to both humans and dogs. The difference is humans know not to eat them. Dogs don't.

Raw eggs can contribute to the possibility of food poisoning from bacteria like Salmonella or E. coli but also, an enzyme in raw eggs interferes with the absorption of a particular B vitamin which can cause skin problems if a dog were to eat raw eggs regularly over time.

Certain kinds of fish such as salmon, trout, shad, or sturgeon can contain a parasite that causes "fish disease" or "salmon poisoning disease." If not treated, the disease can be fatal within two weeks.

Eating too much salt can cause excessive thirst and urination and lead to sodium ion poisoning.

Too much sugar can lead to obesity, dental problems, and possibly the onset of diabetes.

Bread dough left to rise should be kept out of a dogs reach, if a dog ate the raw bread dough it would swell inside and could stretch the dog's abdomen and cause severe pain.

Baking powder and baking soda are both highly toxic to dogs. So are nutmeg and other spices.