The mechanical buttocks may look like a new low for the world of Japanese robotics, but they may actually mark a new leap into the future of humanoid development.
Inventor Nobuhiro Takahashi programmed his creation, called "SHIRI" or "butt" in Japanese, to respond with different emotions to different human touches.
Takahashi hopes to use the proto-type technology to develop responses which can be applied to other part of a robot's body, in particular the face, to help with non-verbal communication.
He decided to develop his technology with a rear end because a bottom's movements are large and make it easier to convey emotion.
"I wanted to try and use a butt to reflect emotions - fear, joy and relaxation," the 24-year-old Takahashi, a graduate student at the Tokyo University of Electro-Communication, told Reuters.
Robots are able to communicate with voices but have largely lacked the sort of non-verbal, physical responses that help power much of human communication. Takahashi hopes his technology can overcome that.
To get a robot to show fear, Takahashi would use a hit, or in the case of the buttocks, a spank.
"Fear is a very human - very living - emotion, so it's expressed with force, with a spank," he said, speaking inside a black tent designed to keep light from damaging the silicon-coated invention.
The robot bottom responds to a hit with quivering. A slow wobble is its default state, the sign for relaxation, while a gentle stroke brings clenches that Takahashi said signal pleasure.
"If we could apply this technology to conventional humanoid robots - these things which are on the dividing line between man and robot - well, they would be able to express feelings sufficient to communicate with humans properly," he said.
(Reporting by Ruairidh Villar; Editing by Elaine Lies and Robert Birsel)