The grooves behind the normal bowel movements may be caused by rectal polyps, hemorrhoids or rectal cancer. 1. Rectal polyp: it is an elevated lesion that occurs on the surface of the rectum, most of them do not have obvious self-conscious symptoms, but if the polyp is relatively large, when the stool passes through the rectal polyp, a groove may be formed. 2. Hemorrhoids: mostly seen in internal hemorrhoids, as the stool passes through the surface of hemorrhoids will lead to the formation of grooves on the surface of feces, and if the stool is relatively dry and hard, it may cause local bleeding when it is discharged. 3. Rectal cancer: Early symptoms are not obvious, but with the gradual increase of tumor, it will protrude into the intestines and form a groove when passing stool. If there is a groove behind the normal stool at the beginning, and if it is accompanied by discomfort (discomfort in the lower abdomen, wanting to defecate, feeling of incomplete defecation after defecation), abdominal pain and other uncomfortable symptoms, one should go to the hospital in time to find out the cause and then target treatment.