In Rick Griffin's Argo, androids are usually designed to look like Funny Animals to avoid this trope, so that humans would be less intimidated by them.
In Dan Abnett's Bequin, Beta finds the Blackwards dolls deeply unsettling due to how highly detailed and lifelike they are, such as the girl doll having a wig of actual human hair. She finds them even more unsettling when they come to life and attack her.
Mr. Beaver: There may be two views about Humans (meaning no offence to the present company). But there's no two views about things that look like Humans and aren't. Mrs. Beaver: I've known good dwarfs. Mr. Beaver: So've I, now you come to speak of it, but precious few, and they were the ones least like men. But in general, take my advice, when you meet anything that's going to be Human and isn't yet, or used to be Human once and isn't now, or ought to be Human and isn't, you keep your eyes on it and feel for your hatchet.
the alloy of humanity that softened the godliness of the youth was lacking in the features of the stranger, awful and immobile in their beauty.
Coraline: Some of the pictures in the novel - especially the picture◊ of the Other Mother with a bug in her mouth.
Played straight in Neal Asher's Cormac novels with the Golem androids. Early in the series most Golem androids are absolutely perfect in their humanoid design, with god-like strength and god-like beauty. Humans are usually pretty disturbed by them in their perfection because it makes the androids feel LESS human, since real humans aren't perfect. Furthermore most non-combat Golems have inhibitors which stop them using their joints in impossible directions and from using strength far greater than even an enhanced human. Subverted when later models have purposeful imperfections (moles, limps, idiosyncrasies) to make them feel more human (but are still quite capable of tearing people, and other androids, limb from limb).
The queen of The Fair Folk in The Wee Free Men is described as looking subtly wrong, because she's too perfect-looking to be human. It turns out her entire body is just an illusion of what she wants the viewer to see.
Look at her eyes. I don't think she's using them to see you with. They're just beautiful ornaments.
Lords and Ladies, notably during the Queen's confrontation with Magrat when her glamour starts to fail.
Lady Myria Lejean from Thief of Time, who is an Auditor in an artificial body created by the Auditors to look human. They don't understand human standards of beauty, but to make her appealing to Jeremy whom they need for their plans, their idea of making her the most beautiful woman alive is copying the features of what was considered the world's most beautiful painting of a woman, then improved upon them by erasing imperfections, adjusting symmetry, that sort of thing. The result is something that Jeremy describes as beautiful, though a "monochromatic" sort of beauty; he first suspects her to be an undead. Even after he gets over it and falls for her, his servant Igor finds Myria highly uncanny as she doesn't smell like an undead - in fact, she doesn't have a smell at all. Also, she "doesn't manage to walk right" as her feet sometimes need a moment to touch the floor after she does a step - because she isn't used to submitting to gravity.
Mr Teatime from Hogfather is the most blatant human example, fittingly since he is a Ax-CrazyProfessional Killer. Teatimes face is actually pleasant however his Glass Eye and fact his other normal eye has a pin-hole-sized pupil making it seem like he looks at world through a keyhole the uncanny effect is invoked. Teatime also moves too fast for peoples liking even the head of the Assassin Guild was slightly bothered he couldnt see Teatime move from the fireplace to the chair in front of his desk. Of course Marc Warren plays him in the adaptation and somehow makes him even creepier.
A couple of novels have this apply to the Doctor, who is, after all, a Human Alien. One instance is after he's fainted at a sideshow:
In Hugos arms, the Doctor hung bonelessly limp, as if he might suddenly flow to the floor in a puddle. Anji had never seen a human body sag like that; no human being had that sort of muscular-skeletal frame. For a frightened instant, she felt more kinship with the man with no limbs than she did with the Doctor.
And one even has a character feel something of the sort applies to the Doctor's human companions, who are fairly ordinary-looking 20th-century Earthlings, as said character is a member of a much more homogeneous future human society:
Their variegated pigmentation, certain small inconsistencies about their facial and bodily forms, evoked a terror in me in some quite other part than if they had been merely monsters. We do not look at a Vlopatuaran land-going octopus or a Wilikranian aerial predatiger and feel quite that fear, I fancy; it takes a man like us in most but not quite, deformed in ways we simply cannot expect, to in this particular manner fright us out our lives.
In-Universe in The Clockwise Man. Due to Melissa's information on how humans looked being inaccurate her face is described as a "parody of humanity", with eyes that seem too human.
The dolls in The Dollmaker appear human (to varying degrees), but they are consistently described, in both appearance and action, as disturbingly other.
Count Dracula is described by Jonathan as having unsettling aquiline features which along with the pale skin, long fingers, pointed teeth and red eyes, which shouldve been enough red flags for him to stop being a polite British houseguest and flee the castle. Dracula looks unnatural even when he de-ages himself; Mina says he isn't good looking with a face that's "hard, cruel and sensual". Later, when fighting Jonathan and the rest of The Team, Drac's movements are noted to be "Panther-like".
The Uncanny Valley effect happens to Lucy and Mina when they get infected with vampirism. Lucy starts off merely sleepwalking, but by the end is gnashing her teeth monstrously when Professor Helsing prevents Arthur from kissing her. As a vampire she is described as being alluring but beast-like when enraged, enough to fill the three men who love her with horror. Mina's process is slower, but even Helsing is freaked out when she unblinkingly watches him sleep with a hungry look in her eyes. Thankfully she is cured before it's too late.
The symbiote-infected humans in Eden Green can heal from any wound; during the initial stages of healing, the area appears mottled and patchy, like pine needles. This is especially off-putting when the part being healed is the head or face.
I could never look long upon a monkey, without very mortifying reflections.
The Fifth Season: The Stone Eaters look like humans made of stone, with diamond teeth, voices that emanate from their chests, and movement that's either achingly slow and deliberate or impossibly fast. Even people who are friends with Stone Eaters are uncomfortable watching them sometimes.
A Fire Upon the Deep. The female human protagonist Ravna is watching a transmission from her homeworld which has been taken over by the Straumli Perversion, an alien with god-like powers. She can clearly see that the human being used as a puppet/mouthpiece is acting strangely, but the aliens with her don't notice anything wrong with him because they're unfamiliar with human body language signals that we notice instinctively. Later this fuels a genocidal campaign to Kill All Humans in the false belief that they're willing agents of the Straumli Perversion.
In Flip-Flop Girl, while attending her father's funeral, Vinnie is unnerved and upset by the wax dummy they put in the coffin to look like him (it's not explained what happened to his real body).
In Frankenstein, this is what triggers Victor's near-immediate rejection of his creation. Victor had selected all of the Creature's body parts to make him as physically imposing and attractive as possible. What he ended up with was a sallow-skinned, sunken-eyed, varicose-veined hulk of a man with serious anger management issues. True to form, the trope kicked in as soon as it started moving. Junji Ito's manga adaptation of the story takes Shelly's words and puts a horrifying face to it, albeit more horrifying.
Played with in the Gaea Trilogy, in which a race of obviously-nonhuman alien centaurs, for reasons that make sense in context, sport genitalia identical to those of humans. This single feature's similarity invokes the Uncanny Valley effect because the rest of the body is so strange.
"Everyone who saw her at the police court said she was at once the most beautiful woman and the most repulsive they had ever set eyes on. I have spoken to a man who saw her, and I assure you he positively shuddered as he tried to describe the woman, but he couldn't tell why."
In Grendel, Beowulf is depicted as being indescribably wrong in some way. Grendel cant think of a way to put it in words. Theres just something off about the way he moves and stands, like hes not entirely human. This is made worse in the climax, where Grendel starts hallucinating from blood loss and perceives Beowulf as becoming a flaming Draconic Humanoid.
The villainous Gray Agents of Sean Cullen's Hamish X series of novels are described as being deep down in the Valley. They seem mostly human, but are completely expressionless, have golden eyes under the goggles they always wear, don't seem to feel pain, and each of their fingers has an extra knuckle.
The Harry Potter series uses the Uncanny Valley to great effect:
If a character acts odd (for example, Ginny's overall behavior in Chamber of Secrets, or teenage Snape walking in a "twitchy manner that recalled a spider" in Order of the Phoenix), keep your eye on him or her. And then, of course, there is the Inferi, which deliberately invoked this trope (because there is absolutely nothing right with a walking corpse). The way Voldemort is characterized in the movie also invokes this trope.
Hell even before Voldermort gives himself his snake-like appearance, he acted unnatural for a boy magical or not. Despite having the handsome features of his father his inner nature contorts his face such as when he learned he was a Wizard from Dumbledore Harry describes his expression as "bestial".
Luna Lovegood is described as having wide, buggy eyes that she blinks less often than one normally would. It helps to augment her strangeness, though she's also a sympathetic friend of the protagonists.
Mad-Eye Moody thanks being disfigured by dozens of fights with Dark Wizards, Harrys first description of Moodys face invokes the Uncanny Valley.
It looked like as though it had been carved out of weatherwood by someone who only had the vaguest idea what human faces look like, and was none too skilled with a chisel.
Barty Crouch Senior has this when he's under the influence of the Imperius Curse, his face is gaunt and skull-like and Harry and Dumbledore think he is unwell. When he partially breaks though the curse, he acts completely unnatural flipping between two personalities: one where he knows what happening and is panicked and the other where he is deluded but ironically acting more sane. Barty Crouch's son has some of this when he's revealed, but the movie where he's played by David Tennant takes it up to eleven thanks to his Maniac Tongue.
Even Big Good Dumbledore has some unsettling traits; his Icy Blue Eyes seem to occasionally x-ray the person they are staring at, and like Luna, he is ridiculously untroubled by most of the events around him. Harry in the first book asks Percy if Dumbledore is mad. Taken aback, Percy tells Harry that hes a genius and the best wizard in the world... but adds that yes, Dumbledore is a bit mad.
Another one would be Ollivander. It's mentioned in his introduction that he almost never blinks and Harry is creeped out by him.
But Bathilda Bagshot takes the cake in the Deathly Hallows, due to her creepy stilted movement, her staring eyes and the fact she moves closer to Harry in darkness and he can't hear her. In reality, she's just a corpse with a massive snake controlling her.
In William Saroyan's The Human Comedy, Mr. Mechano (who advertises a particular brand of patent medicine in a drugstore window) frightens Ulysses so badly that he runs through the streets calling for his family.
The man moved like a piece of machinery, although he was a human being. He looked, however, as if he had been made of wax instead of flesh. He seemed inhuman and in fact he looked like nothing so much as an upright, unburied corpse still capable of moving. The man was the most incredible thing Ulysses had seen in all of his four years of life in the world.
Quasimodo lampshades that his appearance falls into this trope:
... at last he [Quasimodo] said, shaking his heavy and ill-formed head,— "My misfortune is that I resemble a man too much. I should like to be wholly a beast like that goat."
Claude Frollo ain't much better when it comes to this trope due to his Sanity Slippage. Esmeralda describes just being the same room as him as "cold", his face becomes frightening to her and others the more his lust takes over and Frollo's inner conflict degrades his health. This likely a case of Evil Makes You Ugly.
The human-animal things in The Island of Doctor Moreau by H. G. Wells. Just reading about those things is disturbing. Reading about how they're created even more so, as Wells goes into just enough detail about the processes to be even more freaky.
The titular antagonist IT in Stephen King's novel, the genesis of the Monster Clown Pennywise has this trope in spades. Even when he's not transformed and is just talking normally as the clown, IT stares intensely at the children in hunger, plus he has no shadow when the sun is directly behind him all adding to the uncanny. It gets even more terrifying when at one point he has the face of Georgie Denbrough, in a scene that was thankfully left out of the live action adaptions.
James Bond: In Goldfinger, James Bond describes the title villain in this manner. His unease comes from Goldfinger's apparent lack of symmetry—he's like a collection of features that never quite add up to a satisfying whole. His attempt at recreating the man's face on an Identikit machine only adds to his distress.
In Jane Eyre, Jane is the only person who recognizes that something is wrong with Mr Mason: "...I like his physiognomy even less than before: it struck me as being, at the same time, unsettled and inanimate. His eye wandered, and had no meaning in its wandering: this gave him an odd look, such as I never remembered to have seen. For a handsome and not unamiable-looking man, he repelled me exceedingly...".
Invoked in Jugend Ohne Gott, a book written during the Nazi regime, about the indoctrination of the children. The main character (their teacher) constantly comments that several of them stare at him blankly, like fish.
Jurassic Park: After encountering Nedry's corpse, Muldoon takes a look at a nearby Procompsognathus and notices how eerily human-like its hands are, which gives him the creeps.
Naar from Lone Wolf doesn't really have a true physical form, but the one he favors in his inner sanctum is a grotesque misshapen thing. The trait that shocks Lone Wolf more than the others? The dark god has the eyes of a man.
H. P. Lovecraft frequently describes degenerate humans and not-really-humans as looking distinctly off and inherently disturbing, such as the people of Innsmouth, who have fish-person blood. It can be seen as applying this trope, although at least in the more extreme cases his main idea may be not almost-humanness so much as the inherently disturbing eldritch shining through; if there was more of it, it would just be even more disturbing. On the other hand, Lovecraft had fears of degeneration, of the human being too close to the not-human (in "Facts Concerning the Late Arthur Jermyn and His Family", this is played as the ultimate horror), which naturally implies a form of this trope.
Lunars can surround themselves with a Glamour, making most people believe they are much more beautiful than their natural appearance is. However, while the Glamour usually sets the viewers into a state of silent admiration, some are fully aware of it and describe it as highly unsettling and even painful to look at such unnatural beauty.
Besides, Cinder sometimes makes people uncomfortable due to being a cyborg; most of the time, she keeps it to herself, but if needs, she opens up her prostheses or brain implant to adjust wires or link herself to a machine which most people understandably find rather unsavory.
Winter Queen from Malediction Trilogy. To human girl Cecile de Troyes she looks like a very beautiful woman...most of the time. However, from time to time her alienness gets through, and Cecile sees non-human eyes or predatory claws instead of perfect rosy nails.
Most of the anarchist Council of the Days in The Man Who Was Thursday have something fishy about their appearance (e.g. Monday's lopsided smile, Saturday's Sinister Shades or Friday's disquietingly great age) which makes the protagonist deeply uncomfortable. The worst of all, however, is Sunday, mainly because the man is so damned big — he is tall and overweight, but he seems moreover to be out of scale with his surroundings, like (in the narrator's words) a statue carved larger than life-size.
In MARiiMO, Tammy tries to avert this by giving Mariimo a face that doesn't look like a human's.
Name-checked in the Mercy Thompson novels. Mercy describes the vampire Marsilia as being in the Uncanny Valley, as she's unnaturally stiff and still and her facial expressions look like she tried to learn them from a book.
The Steel Inquisitors from Mistborn: The Original Trilogy are described as earily inhuman despite being actual humans who onlyhaving gigantic nails embedded in their eyes! They also have a number of other such spikes in various places around their body (they're actually a form of Blood Magic that gives the Inquisitors various extra powers), and the ones in their eyes are actually long enough to come out the back of their head. They often are depicted in a way that resembles a pair of goggles or teashade sunglasses, which invokes the trope in its own right.
Mostly averted in C. L. Moore's story "No Woman Born". When a noted dancer and actress has her brain transplanted into a robot body after an accident that nearly kills her, she is still able to convey the same sense of beauty, grace, and charisma as before, although she needed to practice moving and talking in her new body before presenting herself to the public. The scientists who worked on her new body decided to give her a blank metal face to avoid the almost-but-not-quite human effect and designed the body to be flexible enough to dance as gracefully she could before, and this is justified in that humans rely on auditory and kinesthetic cues such as voice, gait, and personal mannerisms for recognition, not just appearance. Only at the story's very end, when she lets down her guard for a moment does her voice start sounding flat and robotic, instead of resembling her original body's voice.
In Only Ever Yours by Louise O'Neill, women can no longer be born naturally. They are bred in laboratories as future wives and prostitutes to serve men, and are engineered to be as physically perfect as possible. When protagonist freida and her classmates first meet the Inheritants (the group of boys they were designed for), freida notes the sharp contrast between the naturally born and physically diverse boys, vs the manufactured and artificial appearance of the girls.
In The Pale King, there is something very, very off about Shane Drinion. His odd speech patterns, lack of emotions, facial reactions, or sense of humor make him seem inhuman. There's also the fact that mosquitoes avoid him, he can levitate if he concentrates hard enough on something, he keeps a perfect record of his conversations, and that he can't leave the room without Keith Sabusawa. None of it is explained.
Shapechangers pretending to be humans have this effect in The Power of Five. Of the few that are mentioned, not a single one has maintained their deception for any length of time: One lets his disguise slip when he meets Scarlett, the other has a freakishly round head, one can't speak, one doesn't notice cutting his own thumb off, and one doesn't notice an enormous insect crawling over his eye. The best impersonation so far has been "Audrey Cheng", and even it gave the game away when it forgot to eat. Scarlett rumbled it when she realized the only time she had ever seen "her" express hunger was looking at a fishmonger's slab.
Raptor Red's protagonist and main viewpoint character is a female Utahraptor of the Red-Snout species. A rival species, the Yellow-Snouts, evoke an Uncanny Valley reaction in her: their courtship dance is almost right, but the differences in the motions and in the colour of their snout-band repulse her.
Occasionally this trope's effects are felt in Niven's Ringworld novels, as the many hominid natives fall short of being Human Aliens. Usually it's the ones that are already creepy (ghouls, vampires) which give people the willies when they move their shoulders more loosely than expected or are found to have too small a skull. Also part of the reason our Abusive Precursors are so, well, abusive. Our social system is horrifically twisted due to its rejection of Protector-stage rulers, and we just smell so incredibly wrong.
The GMOs and their offspring exhibit a subtle version of this in Jacqueline Carey's Santa Olivia and its sequel. For the most part they look normal but it's frequently mentioned that when making physical contact for most people there is something subtly wrong and unnerving about them. Their inability to feel fear also means that in some situations their behaviour is off in ways that others find unnerving.
When Akira has his first major hand-to-hand fight, it's mentioned that Alpha is keeping perfectly in his vision no matter how wildly he's moving around, meaning that if someone else could see her in that moment, she'd appear to be flying all over the place despite not doing anything that should move her.
On one occasion, while Akira walks through a crowd, he asks Alpha why she doesn't walk through people, since she's intangible. Instead of explaining, she just walks through some people to show him why not, making Akira nauseous.
Kellhus is completely emotionless, lacks any empathy and is utterly, ruthlessly rational. He can manipulate people by perfectly simulating emotions and normal human interaction. However, at one point he makes a mistake with one character. He takes just a split-second too long to respond to a question, during which his face just goes utterly blank and all emotion leaves his eyes before suddenly smiling and continuing with the conversation. The effect is described as extremely disturbing.
Non-Men. They have human faces described as very beatiful but they are also bald and their teeth are fused together. Not to mention, most of them, called Erratics, are stark raving mad due to their immortality, which overloads their memories.
Sector General: One of the series' main alien cultures is the Kelgians, who are human-sized furry mammalian caterpillars, with constantly mobile fur that expresses their emotions. In one of the later novels, a character is introduced from a different species, which has a similar body plan but black, immobile fur. Apparently, he looks to Kelgians like their equivalent of a Humanoid Abomination.
Serdra from The Silent War is an immortal in her 130s, with a youthful face yet somehow radiates age. Her nearly emotionless demeanor and constantly intense gaze disturbs people, and she tends to let her pupil do the talking to Muggles.
Melisandre is noted as being stunningly beautiful, but there is also something off about her even before her Blood Magic comes into the picture: a subtly wrong shade of red for her hair and eyes with a strangely unblemished, uniformly pale skin for her apparent age and her unrelentingly odd attitude that permeates everything she does and says, for starters. Most men are too afraid of her to give serious thought to sleeping with her, for all most are willing to discuss how attractive she is. There is always a spoken or unspoken "but" attached somewhere. Also, she doesn't need to eat and requires very little sleep. Aware that completely stopping these would make everyone around even more unsettled by her, she acts as if she does.
Seems to be a common trait among the priests and priestesses of R'hlorr — of a certain level, that is. Of the ones we meet, only the cheerfully boisterous Thoros of Myr escapes it. And, that may be because he's only just recently started taking his job seriously after a years-long Crisis of Faith, so he probably has yet to fully acquire it. Well, that or his very stereotypically seedy human side is just a bit too much for it to shine through even with him being capable of jaw-dropping miracles, as yet. By contrast, Moqorro and Benerro do not have to work hard to give hardened fighters and politicians the uncanny collywobbles from the other side of the ship or from across the street even before breaking out the burning people alive thing, for instance.
Out of the Silent Planet examines the trope when Ransom encounters his first nonhuman, and reflects that the hross seems horrifying and deformed when he thinks of it as human, but miraculous and wonderful when he regards it as an animal with the powers of thought and speech.
More straightforwardly, Perelandra features the Un-Man, who is essentially an animated corpse - but he gets even more creepy when you think about what it is that's animating him.
Spinning Silver: In-Universe, the Staryk Fair Folk look normal at a casual glance, but subtly yet profoundly inhuman up close. Miryem finds this much more terrible than an obvious monster would have been.
The short story Stairway to the Stars by Larry Shaw, has this concise explanation: "It — he? — looked almost like a man, and that only made the difference worse."
The Strange Case of Dr. Jekyll and Mr. Hyde: Utterson says that Mr Hyde's appearance gives the impression of deformity without having any. People who look at him dislike him immediately without quite understanding why, though by the end it's clear that his underlying evil causes the reaction rather than any physical property. Adaptations tend to just give Hyde a Nightmare Face however.
Sunshine: Vampires are described In-Universe as human-shaped but wrong in an inherently threatening way, with unnaturally fluid movements, slightly inhuman voices, and a persistent smell of fresh blood. However, they can suppress it well enough to pass for human when they want.
In Those That Wake, Man in Suit evokes this trope, leaving the characters confused and frightened by their inability to describe him.
Shelly from The Troop is constantly described as "insectile" or even less pleasant adjectives. One kid even thinks of him as "something" at one point. Of course, Shelly is a closet sociopath, so it may be the other kid's survival instincts.
"Yes; she had quite a court around her. She would be called very handsome, I suppose, and yet there is something about her face which I didn't like. The features are exquisite, but the expression is strange."
Why is this◊ cover for the Margaret Peterson Haddix book Turnabout so creepy, you may ask? If you didn't notice (some won't), half of the face is young when the other is old, effectively creeping us all out.
TwilightThe description of the vampires' body and skin when one thinks about it. Their skin is beyond eerily pale and their bodies are as hard as rock or diamonds, with the corresponding temperature. Meaning, they are cold as ice to the touch. Their temperature never rises, so no matter how long they may be in a hot climate, they remain like ice.
Scott Westerfeld seems to have a talent for creating things that are Uncanny with a capital U.
The Pretties from the books series Uglies; they're literally perfect with symmetrical faces and all, and they all look very nearly the same. Then there's the specials who add a whole new level of creepy with their "cold beauty".
Lampshaded in So Yesterday. A special effects whiz explains that the human face is the hardest thing to animate convincingly because humans spend almost all of their time reading faces. If it's even a tiny bit off, we won't accept it.
In The Wheel of Time, the Myrddraal are some of the most human-looking Shadowspawn (barring the gholam, which was created to be able to perfectly mimic humans in order to fulfill its function as an assassin, and only turns monstrous when it uses its Rubber Man powers). They're also, however, the most disturbing. It's partly their skin, which is a bit too pale. It's partly the way they move, which is a bit too fluid and makes them look like their joints don't hook up quite right. It's partly the fact that their clothing is always perfectly still, regardless of factors like wind. It's partly their expressions, or lack thereof- Myrddraal never smile and rarely show any emotion that isn't cold-blooded sadism, and there's no noticeable variation in personality between individuals. Oh, and when they lower the hoods of their Black Cloaks, it becomes obvious that they don't have eyes, just smooth skin where eyes should be... but they can still see. Taken all together, they're far more horrifying than the traditionally monstrous Trollocs.
Paolo Bacigalupi apparently has a fetish for girls who fall into this category. The most blatant is the titular character of The Windup Girl, so called because she walks in a jerky manner like a wind-up toy. In-story, this is considered remarkably beautiful, but it's somewhat difficult to visualize how this could avoid falling into the Valley in real life. In-story, it sometimes does. It was also a deliberate design feature to make sure that the main character and others like her couldn't be mistaken for unmodified humans.
In The Witcher novels the elves are described in terms that suggest this trope. On one hand they are extremely beautiful in general terms. On the other, at closer inspection their eyes seem unnaturally large, while their teeth seem too small to their mouths, like adults who still have baby teeth, and they also lack the distinct canine teeth. In result, many humans find elves freaky and disturbing-looking, although the actual reasons for the mutual Fantastic Racism have a bit deeper causes.