At this point, as I was watching the movie, I remembered something from when I was 15. In high school, a former bodyguard gave us a speech about safety and lessening your chances of being abducted. He told us in no uncertain terms that you're more of a target if you're sitting in a broken-down car than if you're roaming the woods. "There aren't any madmen who just happened to be out there waiting for someone to get a flat tire," he said.
In this case, he was wrong -- they should have stayed in the car. The madman in 'The Human Centipede' is Dr. Heiter, a famed surgeon who used to work separating Siamese twins, who now likes to combine people together. And when Lindsay and Jenny ask for help, they get trapped under truly horrific circumstances.
Thus begins what is the most emotionally damaging movie I've seen in a long time. But, if you're a horror fan, you should still brave the theater for it. You won't be disappointed. (Warning: Spoilers below. But I'm so not responsible for any therapy charges you may incur.)