The size and shape of fecal matter produced during a bowel movement do not indicate any medical problems if they are common for the person, explains WebMD. Constipation, diarrhea or any change in the consistency of fecal matter may indicate an infection or a change in diet or activity.
The color of fecal matter often indicates a medical problem, according to WebMD. Black stool can indicate internal bleeding or certain medications or vitamins dispersed through the intestines. Light grey bowel movements may indicate liver disease or a block in the bile flow. Bloody stool may indicate problems with the colon or the anus.