Movie starts with scary guy getting a blowjob from a body less head, then next frame just the head is tossed out the creepy vehicle (van I think). Middle of the movie is like a horror/thriller. End of the movie turns out bad guy has been the main character all along. It takes place in a house in the middle of nowhere. I think it was released 2005-2011

Edit: High Tension was the movie, found it as soon as I asked

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