Colonoscopy is an examination done to look for changes such as swollen, irritated tissues, polyps, and cancer in the large intestine and rectum. During colonoscopy, a long flexible tube is inserted in the rectum. A tiny video camera present at the tip of the tube allows the doctor to view the inside of the entire colon. If there is a need, polyps or other types of abnormal tissue can be removed through the scope during colonoscopy. Tissue samples can also be taken during colonoscopy.