"If you see something that... looks human and isn't, you keep your eyes on it and you feel for your hatchet."Japanese roboticist Masahiro Mori stated in 1970 that the more human a robot acted or looked, the more endearing it would be to a human being. For example, most lovable Robot Buddies look humanoid, but keep quirky and artistically mechanical affectations. However, at some point, the likeness would seem too strong, and it would just come across as a very strange human being. At this point, the acceptance drops suddenly, changing to a powerful negative reaction. When shown as a graph (like the one to the right), the acceptance on the Y axis and increasing X approaching human normal, there is a slow rise, then a sudden drop, then a sudden peak as "human normal" is reached. Masahiro Mori referred to this as the "uncanny valley". This video explains it extremely well. Thus, things that look somewhat human, but are clearly not — such as C-3PO (in Star Wars) or a Golem — produce an accepting reaction, while things that are very nearly human, but just a little strange — such as a child's doll, a ventriloquist's dummy, or a clown — produce a negative response. For some reason the resonance is stronger with a moving object, which is why a corpse is creepy but a moving corpse is creepier still. In fact, some say the very lowest point of the valley is the zombie; though others say that zombies are merely another monster, and that slightly-not-right Pod People, for instance, are closer to the nadir. This applies not only to something's appearence, but to sound as well. For example, a voice speaking words, but at a higher, or lower pitch then is humanly possible, or a recording of a human voice, but played backwards. Or maybe a computer voice like Microsoft Sam. This might explain why we like Ridiculously Human Robots, even if they don't make a lot of intuitive sense. They are just far enough out of the Uncanny Valley not to bother us. This idea has recently been applied to CG effects. While it's become very easy for programs to simulate textures and skin tones, convincing movement and facial expressions aren't always as simple. This can produce an effect where the character comes off as a zombie, if a production company is going for a purely realistic human look. Similarly, many cartoons nowadays prefer a simultaneously stylized yet simplified character design, versus the realistic look amongst some older cartoons. In the latter, it's more obvious the budget just didn't allow characters to move much. Heavily rotoscoped characters also often seem less real than more stylized animated characters, especially when they're in the same production. See the Fleischer Studios version of Gulliver's Travels for an example. This also happens in video games, especially western ones, because the audience in the western world tends to demand photorealistic graphics for their games (or at least that's the perception, sales numbers don't always back this up), while scorning many of the stylized games of the east, which still do use sprite-based games, although there are some eastern 3D games that enter the valley with too detailed graphics as well. (You'll be very hard-pressed to find a western studio that's not Indie or developing for handheld systems that still uses sprites. They're even rarer than studios that use stylized graphics, although some do get a free pass, like Valve and Team Fortress 2.) But this is also extremely indicative of a huge generation gap, where 2D was the ONLY type of video game for two decades, and video games only went from niche to mainstream after 3D was implemented and became a standard, for a multitude of reasons. So sometimes you will get people who have been playing video games for decades missing 2D graphics, the Nostalgia Filter in effect, or thinking a series that started in 2D graphics feels very wrong to them when switching to 3D graphics, creating a total Uncanny Valley. Compare Reality Is Unrealistic, where the poor impression comes less from being 'creepy' as from breaking existing conventions which audiences had come to expect. See also Off Model, Bishonen Line, No Flow in CGI, and Ugly Cute. And while you're at it, see What Measure Is a Non-Cute? as the scientific study of that trope gave birth to this one. An opposite is Eldritch Abomination, where the unsettling effect is caused by being way too unfamiliar rather than being way too human, yet still produces the same abominable effect (although the two can overlap as a Humanoid Abomination). You'll notice that most of the examples in the pages below have to do with inadvertently entering the Valley. This trope can also be used purposely, to make something creepy when creepiness is called for. Some examples of particular ways to produce this effect are listed under Creepily Long Arms, Creepy Long Fingers, Malevolent Masked Men, and Uncanny Valley Makeup.