First theorized by Japanese roboticist Masahiro
Mori in 1970, the Uncanny Valley basically states that the closer a
robot or other nonhuman entity gets to resembling a human, the more humans will like and empathize with it.
However, there is a point in development where humans instead become strongly repulsed by the barely-human
robot/entity. Fortunately, this effect fades as the robot/entity becomes less distinguishable from a human.
Although hotly debated, the theory is present in many sci-fi movies and the like, and has been used to explain people's reactions to some
computer generated characters.