Well, we can add chewing gum to the multitude of things we need to keep away from our dogs. Besides being a nuisance when he doesn't keep his mouth closed, chewing gum can be also be harmful to your dog.  Turns out sugared gum isn't too bad and may just cause a bad tummy ache. However, the Xylitol in sugarless gum can be toxic, and can cause liver failure.  So, if there's a trail of gum wrappers down the hall or your dog is unexpectedly blowing bubbles, get him to a vet right away.