After the fight in the greenhouse, Soo-hyeon breaks Kyung-Chul's left wrist. Yet shortly after, when Kyung-Chul kills the two men in the cab, he grabs and holds back the man in the rear seat while he alternately stabs him and the driver. He shouldn't have physically been able to do this with the wrist broken. Also, it would take six weeks for the wrist to heal, yet Kyung-Chul shows little sign of any impedance in using the left arm for the remainder of the film.
(at around 15 mins) An extra is seen peeking a glance at the camera next to him from under the brim of his ball-cap.