A hard lump in the dog's abdomen may be caused by constipation, tumor or foreign body. It is best to take the dog to the pet hospital for examination. If it is a tumor or foreign body, surgery may be required. If it is constipation, you can use medical treatement. Do not feed your dog food that is not easy to digest, especially bones, which can easily scratch the intestines. If your dog has a bad gastrointestinal condition, you can regularly feed it some probiotics to help with digestion.