Xylitol is extremely dangerous to dogs — doses above 100 mg/kg can cause hypoglycemia, and doses above 500 mg/kg can trigger acute liver failure, because it stimulates a rapid, dog-specific insulin release. It's widely used in sugar-free gum, candy, baked goods, some peanut butters and toothpaste, so always check ingredient labels. Cats, by contrast, show no clear toxicosis even at doses up to 1000 mg/kg and are considered far less susceptible than dogs.