The Uncanny Valley is the uneasy feeling of strangeness people get when they perceive something that doesn't seem quite right. It's a well documented effect where images are similar to what they're supposed to be but are off in some way and more disturbing and uncomfortable to view than something which is completely different and is not subconsciously expected to take on a realistic appearance. For example, people think realistic 3D models of human faces are creepy because they look like human faces but have some small incorrectness of shape, the viewers having the unshakeable sense that there's just something very wrong since the facial expressions are not recognized as normal emotional expressions. It's imperceptibly subtle differences that can alter what emotional effect an object can have. I am not very susceptible to this effect since I think the more realistic looking the better, but I'm very interested in the concept and plan on using it for music at some point. In a case where auditorily or rhythmically something doesn't seem right and is therefore creepy.

There are cases where people have tried and failed to invoke uncanny valley. Namely, I think Mechanical Animals era Marilyn Manson is very pretty.

A precious example of this effect that messed up a lot of people was the creature Dren in the movie Splice, who looks 1/2 pretty girl and 1/2 ugly demon. In the movie, Dren ends up seducing and having sex with the male scientist who genetically engineered her. I'm not going to post that here because I don't want to relive the experience, but it's just hilarious to me imagining the weirdo in the back of the movie theatre who would watch it and actually get hard and then be like, "Yeah man! Oh yeah! This is my shit, man! Oh God! Where is she gonna put that tail!?!?!?!?!?"

I'm gonna post this wholesome dancing scene instead. It gives off what the uncanny valley effect is a lot better than language can.