The Valley of The Uncanny is a phenomenon encountered in Gothic Literature and Art, Robotics, Science Fiction, Dreams, Doll Making, and Weird Fashion.
The Valley of The Uncanny is the dip in the graph between where something or someone is obviously human and obviously NOT human. When something is clearly a robot or doll, it is undisturbing, un-life-like. If someone or something is completely human appearing, that may be creepy, or normal, but it isn't the Valley. The Valley is the point where They MAY be a doll or robot... but you aren't SURE...
It is the Space In Between.
Remember in Blade Runner when you didn't know for sure whether that doll was Pris, --waiting for Decker--, hiding so he'd get close enough for her to kill him? That's it.
A sillier example was in the making of Team America, when the tech crew lip-synching the marionettes did TOO GOOD a job at first at matching the facial movements of the puppets and the voices of the actors. It creeped out the test audience, and the production team had to go back and make the lip synching a little worse before people were comfortable.