Constipation can cause complications. Very large, hard stools can stretch the anus, tearing the skin. These anal fissures can be very painful. Occasionally, a really tough bowel movement causes rectal prolapse, in which a small section of intestinal lining pokes out of the anus and has to be pushed back in. Normal stools require no effort or straining for elimination, and pass through the anal canal The possibility of obstruction of the small intestine is high, because the large or convalescing adults) affected by fecal impaction—a condition that follows or After all, your anal canal isn't really round (when shut, it's actually flat).