Blood in the stool that originates from above the large intestines has a black color. This means that the bleeding originates from either the duodenum, stomach, esophagus and/or mouth. Such bleeding is called "melena". Bleeding from the small intestines, colon and anal opening has a red color and is called "rectorrhagia". In your case, it is difficult to identify the black bits from the description, so you can request a stool sample examination with your primary physician.