National Geographic magazine lists harmful food for dogs and one of them is garlic. It reads "Garlic breaks down a dog's red blood cells, leading to anemia and possible kidney failure from leaking hemoglobin".
There are more interesting facts found in this article about garlic.
Alcohol depresses brain function and can cause coma. So don’t give your dog part of your beer!
Coffee. Caffeine in a cup of coffee is a methylxanthine compound that can increase a dog's heart rate and trigger seizures.
Macadamia nuts. Just a couple can cause tremors, and even temporary paralysis in dog's hind legs
Onions. The damage is cumulative and so small tastes over time can and will
