Some of the latest robots - and even sex robots - look very human, but they fall short of mimicking essential human behavior such as eye contact and complex movement. Researchers theorize that the more human a robot appears to be, the higher the expectations our brains put on it. This creates dissonance when the robot falls short of those expectations of human-likeness.
Although a number of studies have pointed to the existence of the uncanny valley, several others have questioned its existence and have attributed the phenomenon to poor design, and even generational differences in people's response to robots.