There are two general possibilities for a hard lump below the left side of the belly button: if the lump is under the skin, most are likely to be a problem with subcutaneous fat, lipoma, or a subcutaneous tumor. If the hard lump is in the abdominal cavity or appears to change, often with constipation, it may be a clinical condition caused by a fecal mass collecting in the intestine. If the hard lump appears to disappear instead after repeated rubbing or promotion of intestinal peristalsis, it is more likely to be the result of a fecal mass, often caused by slower gastrointestinal motility and poor digestive function. If this symptom is not relieved repeatedly, it is recommended to improve the ultrasound examination and, if necessary, the colonoscopy to further exclude other possible problems. In some cases, routine stool examination can be improved to rule out inflammatory changes caused by poor gastrointestinal motility due to fever, cold or flu.