Colonoscopy is an important screening tool for colorectal cancer. During a colonoscopic procedure, a tiny video camera at the tip of the endoscope generates a video signal of the internal mucosa of the colon. The video data are displayed on a monitor for real-time analysis by the endoscopist. We call videos captured from colonoscopic procedures colonoscopy videos. Because these videos possess unique characteristics, new types of semantic units and parsing techniques are required. In this paper, we define new semantic units called operation shots, each is a segment of visual and audio data that correspond to a therapeutic or biopsy operation. We introduce a new spatio-temporal analysis technique to detect operation shots. Our experiments on colonoscopy videos demonstrate that the technique does not miss any meaningful operation shots and incurs a small number of false operation shots. Our prototype parsing software implements the operation shot detection technique along with our other techniques previously developed for colonoscopy videos. Our browsing tool enables users to quickly locate operation shots of interest. The proposed technique and software are useful (1) for post-procedure reviews and analyses for causes of complications due to biopsy or therapeutic operations, (2) for developing an effective content-based retrieval system for colonoscopy videos to facilitate endoscopic research and education, and (3) for development of a systematic approach to assess endoscopists' procedural skills.