Bonus: Wolf Creek - Head on a Stick
Controversial 2005 Australian horror movie Wolf Creek was criticized for its violence in the US but was also hailed by many reviewers as revolutionary for its brutal intensity and lack of a conventional horror movie structure (surprisingly, a lot of its praise came from English critics on the other side of the world; unsurprisingly, it was nominated for a huge number of awards in Australia).
This scene is probably the most brutal. One of the characters almost escapes from the crazed serial killer's clutches only to be caught up in the old backseat-of-the-car trick (check out that snigger) and end up paralyzed on the floor. The movie's affable Aussie maniac Mick is, oddly, even more disturbing when he's acting friendly. This scene is no exception. The icing on the cake is the way he quotes Crocodile Dundee while stabbing people and severing spines.