I don't think that I need to go in depth with the plot-line, because we all sort of get it. The insane Doctor Heiter preforms a terrible experiment on three unsuspecting humans. I have now watched the film three times, and I have come to realize something interesting about it. And no, I am not referring to Tom Six's research into the complete the medical accuracy.
In the beginning, we witness his tears over a photograph depicting his now-deceased "three-dog". It is obvious from the beginning that this animal was not only a brilliantly successful experiment in his eyes, but also his only companion. He later tells the girls that he doesn't like to be around humans, implying that he most likely does not have too many friends. With the degrees of emotion that he exhibits when thinking about his dog(s), it is obvious that although he prefers to be separated from society, he still desires some sort of companion.
We discover that Heiter was once a well-known surgeon, specializing in the separation of conjoined twins. He moved on past this to practice the reverse - joining life-forms together to create that which he had previously been trained to separate. I think that this is interesting. Instead of separating humans to give them a sense of normalcy in society, he joins them together to create something inhuman.
When Heiter is in the company of the two girls and the Japanese man, he is short-tempered and awkward. He is uncertain of how he should act around humans because he is uncomfortable with their presence. As soon as his creation is complete, his interactions with the three becomes more loving, as a man would treat his beloved pet. He no longer views them as three separate human beings, but instead as a creature with no human capacity. It becomes his pet, and nothing more. This is furthered by the fact that the Japanese man is placed at the front of the line With his inability to speak German or English, he has no way of understanding what Heiter says to him, as well as the fact that Heiter most likely does not understand him. There is a language barrier that disconnects Heiter from his creation, therefore giving it even less human tendencies in his eyes.
The most fascinating part of the film is the art hanging on Heiter's walls. There is not very much attention drawn to it, but if you look at the majority of the work hanging throughout his house, you can see that they resemble the Rorschach inkblots. When you look closer, you see that the images are actually joined twins. Even though it is obvious what these images are, I think the presence of Rorschach-inspired art is notable. The purpose of this test is to interpret the mind of the viewer through what they see in the distorted figures. The interpretations made are fabricated completely by the individual viewing them, and this is considered to be a look into the brain and the way that it functions for that specific individual. The fact that Heiter has these works hanging throughout his house calls attention to his interpretations in his own life. He takes these three humans, and disregards the truth of what they are. They becomes nothing more than a dog-like creature to him, and he refuses to view them in any other way. The fact that the audience is so disgusted by the situation calls attention to the fact that he is not disturbed at all. He only sees what he wants to see.
And if you ask me, this insane doctor only sees his sweet "three-dog" that he misses so very much.