The banana peel is not poisonous to dogs if eaten in limited quantities. However, they are difficult to chew and digest and there could be a risk of diarrhea or vomiting which could lead to an upset stomach or intestinal blockage. If you think your dog has consumed a banana peel, keep an eye on their bowel movements for a few days and look for indications of gagging or choking. If they don't vomit or pass the banana peel, take them to the veterinarian. If your dog has eaten many banana peels, see a veterinarian right away.