While it is certainly possible that tobacco could kill a dog, it would most likely take quite a large amount of tobacco to have this effect. Dogs are much smaller than humans, so they would require less tobacco to reach a lethal dose. However, dogs also metabolize nicotine much faster than humans, so it is possible that even a small amount of tobacco could be harmful. Symptoms of nicotine toxicity in dogs include vomiting, diarrhea, increased heart rate, difficulty breathing, and seizures. If your dog has ingested any amount of tobacco, it is important to seek veterinary care immediately.