Garlic kills dogs because thiosulfate damages red blood cells. Some breeds are sensitive to garlic, but it takes a lot to poison.
Iron-containing vitamins can damage dogs' kidneys, liver, and digestive systems. Prenatal supplements are harmful because they contain more iron than regular vitamins.
Avocados are harmful because of persin, a fungicidal toxin. Smaller amounts can cause vomiting and diarrhea, but only excessive dosages are deadly.
Small doses of mustard won't kill dogs, but high levels are hazardous. Vets commonly recommend mustard to induce vomiting due to its moderate toxicity.
Amygdalin makes apple seeds toxic, but the flesh is safe. These must be chewed and swallowed in big numbers to be toxic.
Sugar substitute xylitol is found in candies and baked goods. It's highly poisonous to dogs, producing fast insulin release and unconsciousness in 15–20 minutes.
Raw bones are fine for dogs, but avoid cooked ones. These readily splinter and can induce deadly constipation or perforation in big quantities.
Milk and dairy products promote calcium, but they also cause lactose intolerance in dogs. Canine discomfort can result.