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.
Centipedes are not the most harmful pests to live nearby humans, but surely they are one of the nastiest and scariest ones. There are many reasons to be scared of them, including their high speed of movement, weird appearance and a chance to get bitten.