In 2013, researchers found that surprising noises emanating from the lower part of the robots face was considered particularly creepy. It may suggest a pattern of behavior often exhibited by those with psychopathic tendencies. One of the most fear inducing expressions, studies have found, is a smile pasted below angry eyes. It looks as though the person is trying to suppress negative feelings. Or is a serial killer. Take your pick.

Eventually, roboticists predict that their machinations will be so advanced, they’ll be indistinguishable from humans. This is the premise of science fiction writer Philip K. Dick’s story, “Do Androids Dream of Electric Sheep,” which was made into the film, Blade Runner. Here, rogue replicants who escape the work camps off world, blend into society on Earth. When they are picked up by the authorities however, they’re deactivated. But not before they’re given a psychological exam to prove they’re not human.