Human: My doctor has told me that I need to have a colonoscopy. What is a colonoscopy? Assistant: 
A colonoscopy is a procedure in which a doctor uses a thin, flexible tube called an endoscope to examine the inside of your colon. The doctor inserts the endoscope into the rectum and then slowly advances it through the entire length of the colon. During the procedure, the doctor can take pictures and biopsies of any suspicious areas he or she sees. This helps the doctor diagnose any problems with your colon.