Hello Dileep, One quick hint, Chew food properly before swallowing. Reqarding black coloured stools - need further evaluation to know whether you have pain abdomen, bloating sensation , Gastritis/ Gerd symptoms. So I would suggest for proper evaluation meet the physician or gastroenterologist or a general surgeon. You might require endoscopy to evaluate your Gi system. A physical examination by above specialist can help to decide further action.