Mothballs can be toxic to pets. Mothballs are generally used to repel moths that destroy clothing. Mothballs contain naphthalene or paradichlorobenzene and can be formulated into cakes, balls, or flakes. As little as one mothball can potentially result in significant illness in a small dog or an average-sized cat.
Keep all mothballs stored away from your dog. Depending on the amount ingested and the size of your dog, signs of toxicity include: lethargy, weakness, vomiting, diarrhea, abdominal pain, lack of appetite, seizures and/or coma.
For more information mothball ingestion, please read Moth Repellent Product Poisonings