"Within 30 minutes of consuming a small amount of a xylitol-sweetened product, the ASPCA says, dogs can experience a dramatic drop in blood sugar, and they usually begin vomiting, become lethargic and can have difficulty standing or walking. Some have seizures, develop internal hemorrhaging and lesions and suffer liver failure. As few as two or three sticks of xylitol gum could be toxic to a 20-pound dog, the ASPCA says."
https://www.usatoday.com/news/health/2007-03-18-xylitol-sweetener_N.htm
https://www.usatoday.com/news/health/2007-03-18-xylitol-sweetener_N.htm