In the club scene where Young-taek kills the lesbian, he grips her head below her chin and starts cutting her ear. In the next shot, a close up, his grip on her face and the knife has suddenly changed and he hasn't started to cut her ear off yet.
When Detective Kim finds the severed finger, the actor didn't hold the pose long enough, so the frame is noticeably frozen to lengthen the shot.
The English subtitles on this movie are horribly inaccurate. For example, instead of saying that the killer "cut out" or "removed" the fetus, the subtitle states, "he excavated the embryo."