Wikipedia says a poltergeist is “an invisible spirit or ghost that manifests itself by moving and influencing objects”. And it’s supposed to scare people. Japan’s Keio University and the Kyoto University of Art & Design, however, didn’t quite understand and developed a very physical poltergeist in their lab, which doesn’t fit all criteria.
Their Sukima Robotto (interspace robot) essentially consists of a pair of eyes and arms that are attached to an ordinary desk and connected to a PC via bluetooth. Human presence sensors make sure that the eyes and arms start moving towards the person approaching the robot.
The scary special effect is provided by a a foliage plant and hairs shaken by artificial wind from a ventilator. If you think that doesn’t sound convincing, you are right (just watch the video below).