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.

The unnaturally wide gap between breasts
"enhanced" with artificial implants.