Old Boy comes to my mind, this is absolutely not the movie with the most shocking scenes from a pure "visual" point of view, but it has some subtle disturbing feelings in many points, like this:
DON'T watch it if you're an animal lover (well, a fanatic animal lover...) or you are easily disgusted, all people who watched the movie will understand what the clip is about after this "disclaimer"
http://www.youtube.com/watch?v=KuTzeJbP_6s