Penetrating trauma of the colon is usually diagnosed intraoperatively and missed injuries cause considerable morbidity and mortality. Herein, we described an intraoperative diagnostic method for invisible openings on the colon due to a birdshot injury. A 30-year-old man was admitted to the hospital after sustaining gunshot pellet injuries to his abdomen, back, and extremities. Emergency laparotomy relieved splenic injury and free pellet fragments in the abdomen. A pellet fragment was also palpated in the descending colon. Despite meticulous inspection of the colon, it failed to show the entrance of the pellet. An 18F catheter was passed through the anus and was connected to a CO2 insufflator of the laparoscopy unit. The abdominal cavity was filled with normal saline and 1.5 l of CO2 was inflated into the rectum. Five tiny (2-mm) openings on the retroperitoneal part of the descending colon were demonstrated with the help of the air bubbles. All of the openings were suture-ligated and his postoperative course was uneventful. We believe that inflating the colon in cases of abdominal birdshot injuries may allow the demonstration of tiny perforations and provide immediate repairs of missed injuries.