Under intravenous sedation or general anesthesia, a colonoscope is inserted through the anus to the rectum while the person is lying on the side, then advanced through the colon. After inflation with air or carbon dioxide to stretch the large intestine to allow easier visualization, the colonoscope is slowly removed while its flexible tip allows for inspection of the inner lining of colon and rectum. There may be discomfort when inserting the colonoscope. Any suspicious changes of the lining can be biopsied, and if a polyp is spotted it can be removed (polypectomy) with a snare and cautery (a hot instrument). Biopsy and polypectomy are not painful. The biopsy tissue and the polyp are later examined under a microscope. Colonoscopy usually lasts less than 30 minutes but it may be longer if any additional problems like multiple polyps or bleeding require treatment.