<s>[INST] I passed 4 brown/black fibrous things about 1/2 inch long in my stool. There isn t any blood. I did eat some blueberries yesterday, so I was wondering if that could be what they are. My father is 74 and is battling colon cancer so I am a little concerned. [/INST] hi, ur age should be known to me. history of colon cancer in ur father put u on high risk for the same. black thing in ur stools is a matter or concern, if u have not taken any thing unusual in food. get a fecal occult blood testing done. if it is positive u should undergo colonoscopy and upper GI endoscopy. if it is negative, u should have a screening sonography of abdomen and colonoscopy at an age of 50 years or as symptoms indicate. </s>