Centopeia Humana -
Specifically, the antagonist (Dr. Heiter) cuts the ligaments behind the knees of his victims so they cannot stand, then surgically attaches the mouth of the second person to the rectum of the first, and the mouth of the third to the rectum of the second. The "centipede" is then forced to eat and defecate as a single chain.
The phrase "centopeia humana" (Portuguese for "The Human Centipede") refers to the horror film series by Tom Six. The most defining feature of the first film is: centopeia humana