<human>: I've been told that I need to have a colonoscopy. What is it and why is it necessary?
<bot>: A colonoscopy is a procedure that involves the insertion of a thin tube into the rectum, which allows the doctor to view the inside of the large intestine. It can be used to detect polyps or other abnormalities in the lining of the colon. This can help diagnose certain conditions such as cancer, inflammatory bowel disease, and colitis.