A man lying flat on his left side of the abdomen with a hard thing, may be related to constipation, colon mass, abdominal mass and other reasons, need to be further differential diagnosis by a doctor. 1. Constipation: If fecal matter accumulates in the intestinal lumen of the sigmoid colon, a hard object may form. 2. Colon swelling: such as colon cysts, colon cancer and other causes may appear in the lying down can be touched a hard thing phenomenon. 3. Abdominal mass: If the tumor is large in size, such as lipoma, there may be a hard object on the left side of the abdomen. It is suggested that patients who have a hard thing on the left side of the abdomen when lying down should go to the hospital in time to clarify the cause of the disease and carry out standardized treatment under the guidance of the doctor, so as to avoid delaying the condition and bringing adverse effects to the body.