The vast majority of people with mental retardation have IQ levels of 55 to 69 and are considered mildly retarded. Mildly retarded children often go undiagnosed until they are well into their school years. They are often slower to walk, talk, and feed themselves than most other children.
When Tom Six began creating the Human Centipede sequels, he envisioned a trilogy that works as a movie centipede. Each sequel opens with the ending of the previous film, as the events of that film influence said sequel.
The main tagline of the first Human Centipede film is 100% Medically Accurate. Director Tom Six had stated that he wanted the surgery to medically possible in real life. He consulted a real surgeon in Holland, who at first didn't want to help out with the idea due to his Hippocratic oath, but later changed his mind as he feels that film is an art form.