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Human Outside, Alien Inside

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Image by euclase. Used with permission.

Kim: I've got to be honest, I wasn't expecting something so different.
Tal: Neither was I. Our species look so similar... well at least on the surface.
Kim: I would've never guessed when it came down to the basics. Well, let's just say the birds and bees will be very confused.

Let's face it: Building a truly elaborate alien costume costs money, more than the budget will safely allow. However, Rubber-Forehead Aliens, cheap as they are, just won't cut it forever.

One safe way to get around the latter problem is to suggest that while on the outside they're exactly the same, on the inside of your alien, anything goes. If you were to dissect the average TV alien, it would look like someone had torn a squid apart and stapled it to the remnants of a rump roast.

Once this is done, the alien sounds suitably... alien-y. Of course, now the producers have to make sure the creatures are gutted only off-camera.

This not only applies to physical organs, but biochemistry as well. Funny colors of blood, odd allergies, complicated mating rituals (or mating organs), Bizarre Sexual Dimorphism, funky dietary requirements (or intoxicants) or interesting bowel movements are all common. Sometimes even their minds are totally different, making communication with them problematic.

The less human-looking the alien is outside, the less likely this trope will be resorted to. This can lead to the ironic trap of Serkis Folk and other more elaborate aliens falling on the other side of the Uncanny Valley and thus seeming, on some level, more human than the Human Aliens or Rubber-Forehead Aliens if they appear in the same series.

Aliens may also be shown to have immunity from things that are plenty lethal to your average person, being able to survive heat and cold extremes unprotected, tolerate massive doses of radiation, being a living bulletproof vest, or be unaffected by poisonous materials. On the other hand, they could also be negatively affected, or perhaps even injured or killed, by a substance that would be completely harmless to an Earthling.

Interestingly, this isn't inverted very often. Humans, even when they're the "aliens" of a story, almost never have flashy biological differences that make them anything but weaker than the rest of the cast.

For more literal and squicky examples of an alien "inside" a human, see Mobile-Suit Human, Genuine Human Hide, and Puppeteer Parasite.


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    Anime & Manga 
  • Ayakashi Triangle:
    • While working their way up the Bishōnen Line, jinyo go from pitch-black humanoids to completely human-looking, but the latter form appears to be only skin-deep. Whenever injured, their human-like flesh cracks like stone to show the same blackness beneath.
    • Defied when Matsuri is cloned and Reo tries to identify which is the original with a medical exam, but she's surprised to find both are human on the inside as well. Kanade points out that, while Suzu's omokage is Made of Bologna, they can be made anatomically accurate even on the inside. Further testing shows both Matsuris have spiritual energy the same as a human as well.
  • Parasyte: The eponymous Puppeteer Parasites leave their hosts bodies outwardly unchanged most of the time, but alter their biology even when not using their Lovecraftian Superpower. Apart from their Body Horror-riffic maturation process, they can split their body mass into multiple pieces (although pieces that are too small will wither and die quickly), they're made of a singular type of cell that they can turn into any variety of bodily tissue they need, fire and acids cause them to undergo the equivalent of a grand mal seizure, and they don't know how, or even IF they reproduce.
  • Urusei Yatsura:
    • One chapter/episode features Lum and Ten eating pickles and realizing too late that the brine has an effect on them that alcohol does not.
    • In the first chapter of the Dracula storyline (Anime episode: "What A Dracula"), it is revealed that the Oni can't stand the smell of garlic and are repulsed by those who've eaten it. Ataru explicitly compares Lum to Dracula after proving that, yes, his garlic-scented breath does act like tear gas on her, going so far as to jokingly try and ward her off with a cross after pointing out she hates garlic, has fangs, and bites his neck/sucks his blood.
  • The natives of The Twelve Kingdoms are apparently indistinguishable from Earth humans, but instead of reproducing "normally" they are born out of large fruit that grow on special trees. They can have sex, but it looks like it's for fun and not for reproduction.
    • It doesn't end there: Sometimes still-growing egg-fruit accidentally fall from their branches and into shoku (storm-induced portals to the real world), where they are "somehow" transported into the wombs of pregnant human women. That's how Youko Nakajima, the main heroine, was born.
      • Lampshaded in the novels, where Rakushun admits that the concept of the eggs being transported from the middle of the ocean to a person womb is bizarre.
  • The inhabitants of the world of Simoun are otherwise indistinguishable from Earth humans, except that they're all born the same sex, develop feminine bodies when they reach adolescence and choose a sex at age 17 by wading through a particular spring. Reaching such a state through evolution is extremely unlikely, but this is a fantasy/steam-punk series that needs a justification for making all the main characters lesbians.
    • Simoun is carrying on in the grand bizarro-feminist tradition of Doris Lessing, in whose The Cleft (which actually came out a year after Simoun) someone being born male nearly destroys the primordial human race.
    • The track names of the OST suggest a Gendercide of unspecified origin or nature.
  • In the decidedly more mature manga version of Mermaid Melody Pichi Pichi Pitch, mermaids can get drunk on anything carbonated.
  • The Goddesses from Ah! My Goddess could fall under this. Urd uses alcohol as an "alternate energy source", but seems to suffer no deleterious effects. Skuld is the same with ice cream. Belldandy can drink a distillery and be completely unaffected, but gets blitzed off of soda. This just makes her an even sweeter and more empathetic Literal Genie.
  • Invoked in the 21st episode of Irresponsible Captain Tylor, "Paco-Paco Junior". Having gone to sleep beside Tylor at the end of the last episode, Azalyn/Empress Goza XVI claims that she's pregnant with Tylor's child, due to the differences of the Raalgon biology compared to those of the human. She's lying, as the crew finds out by the episode's end.
  • Parodied in Kenichi: The Mightiest Disciple with Nijima, who apparently has some biological irregularities.
  • Used to a small degree in Boku no Futatsu no Tsubasa, in which members of Makoto's dad's species are all hermaphrodites, for starters. In an inversion, it's subtly implied that humans are a fair bit hornier in general.
  • Celty in Durarara!! has most of the same organs as a human, but they're vestigial and nonfunctional (to the bewilderment of a character who vivisects her).
  • The Homunculi in the manga and 2009 anime of Fullmetal Alchemist. They look human, possess skeletons and muscle systems, but they have no internal organs. Instead, they all have a Philosopher's Stone at their core. This gives them the power to heal from even small pieces of body tissue as long as they have souls to draw power from. Many of them have been alive for centuries. Each Homunculus also has a unique power of their own. They're all recognizable by the Ouroboros tattoos they each have somewhere on their body.
  • The Ghouls of Tokyo Ghoul have black eyes with red pupils whenever they reveal their true nature, but are otherwise externally indistinguishable from humans. They can't feed on anything besides water, coffee, and human flesh; all other foods taste repulsive to them and will even poison them if they try to ingest it. Ghouls also naturally possess superior physical attributes to humans, including a Healing Factor, a system of Rc cells that function almost like a "liquid muscle", and a hunting organ/extra limb called a Kagune, which can manifest one of many different weapons. Ghouls can also mutate their kagune into a stronger form by eating other Ghouls. Despite these biological differences, Ghouls and Humans share enough genetic similarity to make organ transplants and interspecies reproduction possible.
  • Rimuru Tempest of That Time I Got Reincarnated as a Slime has the ability to transform into anyone he's absorbed via "Mimicry" and his Shapeshifter Default Form is a human form, but he's still a slime at the end. On the rare occasions he's taken direct physical damage, his skin was torn to reveal the blue slime underneath. It's implied he could take the mimicry even further to transform even his internals to that of his target, but there's just no practical reason to do so.
  • Downplayed in Miss Kobayashi's Dragon Maid. Dragons use magic to take on a more or less human form, but things like their metabolism and blood pressure are vastly different from humans. This ends up becoming an issue for Elma when she attends a fasting dojo in her spin-off, and needs Lucoa to come along and fudge her test results so they won't realize that anything is out of the ordinary.

    Comic Books 
  • An alien woman in an old EC Comics title did in her earthling husband on her wedding night after seeing his navel and realizing he was a mammal. This entirely Caucasian-looking blonde-haired woman with nice, perky breasts was supposed to be from an egg-laying species who find the mammalian lifestyle disgusting.
  • Superman has many hand waves for his many powers, but the main thing to consider is his Kryptonian ability to emit microwave radiation and levitate, all from exposure to higher-energy solar radiation. At least one story showed with an X-Ray scan that his internal organs don't resemble a human's at all.
  • Most if not all of the Legion of Super-Heroes must fall into this category, Triplicate Girl/Duo Damsel and Matter-Eater Lad being two of the most obvious examples.
  • In Sergio Aragonés' "A MAD Look At Star Wars", Luke Skywalker is in Mos Eisley, and asks to use the bathroom. In there, he finds several different varieties of urinal.
  • A rare inversion: The three-eyed altered humans who show up in a few issues of Tom Strong can no longer eat at least certain terrestrial foodstuffs without getting the pukes. However, coffee doesn't bother them... and normal humans seem to be able to eat their food without adverse effects.
  • Some aliens in Empowered have two left kidneys. And one kind of alien (maybe the same one) has kidney equivalents that filter the bloodstream using coherent light — essentially, Frickin' Laser Beams.
  • Marvel Universe:
    • The Kree have black-widow-like mating practices; females are "neutered" to prevent this. They also require a special gas or other life-supporting technology to breathe on Earth.
    • Karolina Dean and family from Runaways. On the surface they look like normal humans, but their bodies apparently store and then expel solar energy and a dying vampire notes that Karolina's blood "burns like sunlight". This never being picked up by a doctor could be explained by her parents' apparent natural living kick, which might have involved never taking Karolina to a doctor or having her vaccinated.
    • Teddy Altman from Young Avengers is a Skrull-Kree hybrid; while his default form is that of a pink Kree (essentially a Caucasian human), his internal organs are those of a Skrull. It saves his life while being tortured, as during the vivisection, his internal organs kept rearranging themselves to avoid being cut even with Teddy being unconscious.
    • Mutant powers will on occasion be cursorily explained with physiological differences. Mutant psychics will be said to have different brain structures, while mutant speedsters like Quicksilver or Whirlwind will have explanations detailing the Required Secondary Powers needed to survive their speed; the latter even being said to have body fluids that are thick like motor oil.
    • The Ultimate Fantastic Four series uses some decidedly non-human anatomy to explain some of the team's powers. Reed, for instance, looks fully human when not using his stretching powers, but no longer has internal organs, merely possessing a "bacterial stack" in its place. Oh, and he no longer craps.

    Fan Works 
  • In The Butcher Bird, much like the example given in Tokyo Ghoul, ghouls all typically look human unless they put on their Game Face. In addition to this, Augments, barring the Cogs and Oni, generally look mostly human - even the eight foot tall Lightning Bruiser Wolves aren't outside the appearance of humans in the world of One Piece, and the other Augment types give little indication of their abilities.
  • Child of the Storm has Asgardians, pink Kree and Kryptonians all looking very human on the outside - of course, since all three of those species are considerably older, it is probably the other way around.
    • Also, all three are considerably stronger than the average human, to varying degrees, by various means: Asgardians are living magical reactors, the Kree are evolved in higher gravity and Kryptonians absorb solar radiation.
    • This (in the case of the Kree and the Kryptonians) also probably has quite a lot to do with the Celestials and their seeding the universe with life, using the same basic model.
  • It's Fanon and the subject of at least one fanfic (probably more) that Vulcans get drunk on chocolate.
  • The Overlanders from Always Having Juice tend to look very human... save for the functioning hands made of hair, giant noses, occasional lack of a head, Amazing Technicolor Population of pink to blue to pure white, and that's not even getting into how their bodies work on a molecular level, and how they are evidently adapted for colder climates without having to walk around covered head to toe in warm clothing.
  • In Chapter 18 of Origin Story, Alex Harris (a Kryptonian) discusses the physical differences between humans and Kryptonians with her human lover, Louise Fulford. Among the differences Alex mentions are the location of the Kryptonian heart (its center right, as opposed to being center left, like in humans), the lack of anything resembling an appendix, one fewer set of molars, a menstruation cycle that occurs only once every three Terran months, and fewer body hairs per square inch of skin. Alex also notes some differences that make humans superior to Kryptonians — or would, were it not for Earth's yellow sun turning Kryptonians into Physical Gods. Things like Kryptonians being more susceptible to environmental allergens, and having eyes that weren't as sensitive to shades of color than a human eye.
  • In Hard Being Pure, Noa's mutation changes her such that her bones are an alloy of Orichalium and Mythril, her whole body substitutes for her brain, and she doesn't bleed since her flesh is more like synthetic plastic than living tissue.
  • Played with in Neither a Bird nor a Plane, it's Deku! Izuku's organs are close enough to a human's that he has no problems passing his medical exams without arousing suspicion. But he can't bring himself to hurl even though hearing the story behind All Might's grievous injuries made him sick to his stomach and brought back memories of when he scarred Bakugou. He also wonders if he's capable of having a heart attack after his heart metaphorically threatens to leap out of his chest as he watches the Sludge Villain rampaging in front of him. He then wonders if he even has a heart in the first place, though this is played more for dramatic effect to illustrate his lack of self-esteem than to be taken literally.

    Films — Live-Action 
  • Galaxy Quest:
    • The cephalopodic Thermians use holographic projectors to Cosplay as human. When one of the humans, Fred, falls in love with a Thermian, she deactivates her holoprojector, and they proceed to do something that makes Plucky Comic Relief dude Guy exclaim "Oh, that's not right!"
    • Played with in the Thermians' sincere but stomach-churning attempts to accommodate the perceived needs of "fellow extraterrestrial" Dr. Lazarus, who is actually a human actor. A deleted scene on the DVD has a Thermian showing "Dr. Lazarus" to his quarters, where there is a large bathroom equipped with bizarre fixtures. "You're very... complicated," the Thermian explains.
  • Men in Black:
    • A literal example of human outside and alien inside are the Arquillians; diminutive aliens inside human body suits.
    • Kay shows Jay that aliens do exists by blowing up a Pawn Shop Owner's head. The alien looks exactly as a human but his head regenerates. (In the animated series this is expanded as the ability to regenerate the entire body).
  • In My Favorite Martian, it is made clear that the Martian gum only changes the outward appearance of whoever is chewing it, leaving any major organs or other special biological properties (such as Martin's three stomachs and the "Martian Depression") intact.
  • In Star Trek VI: The Undiscovered Country, after a "welcome fight" that Kirk has with another Rura Penthe prisoner:
    Kirk: I was lucky that thing had knees!
    Martia: That was not his knee. [Kirk does a Double Take] Not everyone keeps their genitals in the same place, Captain.
    Kirk: Anything you wanna tell me?
    [Martia smirks and puffs on a cigar]
  • Played with in TRON. Programs and Isos resemble humans. Even more specifically for Programs is that they sometimes are a doppelganger for the human who coded them. But when they are wounded, it looks like hunks carved out of their bodies, scars resemble dead pixels on a monitor, and serious or lethal wounds cause them to shatter like safety glass instead of bleed. They feed by drinking energy, and it's implied that their circuitry is very sensitive.
  • The aliens in What Planet Are You From? are just like humans, with only two differences: 1) everyone in their society is male; 2) their bodies can produce shafts of light.

  • In The Alien Series, Alpha Centaurion may look human, but their internal organs are radically different. For one thing, they have two hearts.
  • The aliens from Anathem cannot metabolize food from the planet in which the story is set, and can only marginally breathe the air. This isn't primarily because they respirate something besides oxygen, or because the foods they eat aren't composed principally of sugar, protein and fat, but rather because they're from a different universe where the atoms are shaped slightly differently.
  • In City of a Thousand Suns by Samuel R. Delany, an alien is described as looking exactly like a human woman, but "[i]nternal examination and genetic analysis would prove her a bisexual species of moss".
  • A fairly subtle example: In the Confederation of Valor series, Taykans become mature physically, sexually, and (to a limited extent, at least) socially long before they become fertile.
  • Scott Adams' non-fiction book The Dilbert Future is a realistic approach to predicting the future, with mankind's obvious faults taken into account. One section criticizes the idea that humans could have sex with aliens like in Star Trek. Scott's own speculated attempt is summed up with this delightful passage:
    Me: May I touch that?
    Alien: That is not an erogenous zone. It is a separate corporeal being that has been attached to my body for six hundred years.
    Me: It's cute. I wonder if it would let me have sex with it.
    Alien: That's exactly what I said six hundred years ago.
  • Everworld: The heroes get to see a satyr chopped in half. Nothing drops out, and his body is basically described as containing vague shapes instead of actual guts. The satyr himself doesn't seem too offput by the experience, he's last heard complaining that all the wine is just falling out of him, while the lower half follows the heroes and is eventually bartered for entry into the fairy's stronghold.
  • In InCryptid, cuckoos are biologically a species of interdimensional telepathic wasp, but outwardly appear human (always the same human, only differing in age and gender). Their Bizarre Alien Biology includes a decentralized circulatory system and clear blood (which is a natural painkiller and antibiotic).
  • In John Carter of Mars, it's not really gone into much, but this is the case for Red Martians (and presumably the other three humanoid Martian races) — though they look superficially human, they reproduce by laying eggs, live for hundreds (potentially thousands) of years, can survive extended periods without food or water (handy for living on what's largely a desert planet) and, in The Film of the Book, have bright blue blood. Oddly, this somehow does not prevent John Carter and Red Martian princess Dejah Thoris from having two kids.
  • Lilith's Brood goes at length to describe just how inhuman the Oankali are to humans. For starters, they see, smell, and hear through hair-like tendrils all over their body. One that's met early on was bred specifically to look human... meaning that those tendrils are in the spots normally occupied by the eyes, ears and nose. Let's not even get started on how they mate. They're also three-gendered... and the third gender has a second, boneless pair of arms... and that's just the most externally obvious and least bizarre trait.
  • In A Lord from Planet Earth, the entire galaxy is populated by Human Aliens, many of which look nearly indistinguishable from humans. In fact, the main character (a human) meets and later marries a woman from planet Tar, who easily passes for an Earthling. Other races have slight differences in external features, but may have radical differences internally. For example, Palians look like pale humans with elongated canines and yellowy eyes. They also exclusively consume blood and are sensitive to certain radiation emitted by yellow dwarf stars. Their visits to Earth resulted in the vampire myths. Another race has blue skin and is a lot less sensitive to extreme temperatures. The author explains it all with Panspermia, as all races in the galaxy but one are a product of seeding their homeworlds by the aptly-named Seeders. The various internal differences are simply the result of the same DNA evolving differently due to the various environments present on each planet. In fact, this forms the main plotline of the trilogy.
  • The Machineries of Empire: The clone of Shuos Jedao turns out to be a voidmoth grown into human form — human enough on the outside to fool even himself, but a mass of infinitely regenerating tentacles underneath. When a grenade blast strips the skin away, he's a writhing humanoid outline of solid shadow.
  • Most of the Marra encountered in The Madness Season like to disguise themselves as human. Though this is mostly because the hero tends to visit human colonies rather than those of other intelligent species. They may superficially seem human, but an FMRI shows some major differences.
  • The classic L. Sprague de Camp short story "Nothing in the Rules" has a mermaid who gets drunk on fresh water, which would be fine if the protagonists hadn't just entered her into a swimming meet (hence the title).
  • Prince Roger: Inverted in March Upcountry. Aliens poison the food of a squad of human soldiers and try to blackmail them with the antidote. Not only is the poison tasteless to the aliens but strongly flavoured to the soldiers, it also turns out to not affect humans. In a further inversion, the human's doctor discovers another poison (an obvious stand-in for fugu venom) can be used to produce the several nutrients the humans need for their own health, but they hadn't been able to find up to that point in the planet's flora and fauna; and just in time, as their reserve of supplement pills were running out. Their gender also causes confusion. The 'males' are smaller and act as Mister Seahorse carrying the young to term. The 'females' are larger and have a very pronounced ovipositor. Consequently, the gender responsibilities in the society are switched relative to human society. When they figure this out, the humans get very confused before eventually deciding to keep calling the females males and males female to avoid confusion.
  • The Stardoc series thrives on this. Just to give a relatively tame example: Jorenians (large, attractive, blue-skinned humanoids who can actually interbreed with humans) have green blood, twelve-chambered hearts, retractable claws, compartmentalized stomachs, and an unusually large and complex spleen (which is a vital organ to the species).
  • Star Trek Novel 'Verse
    • The Starfleet Corps of Engineers stories do this while fleshing out the Ardanans, who were established in Star Trek: The Original Series as looking just like humans (as did many of the series' aliens). The SCE stories describe the Ardanan brain and demonstrate that its structure and chemistry is very different from that of humans; this becomes a plot point.
    • A Singular Destiny mentions that Zaldans (who look human other than their webbed hands) have a different internal layout.
    • A multiple-personalitied alien race are described by Diane Duane in Spock's World; they have "octocameral" brains, so they have eight personalities each.
  • Stories set in the Star Wars Legends and Star Wars Expanded Universe universes often describe the unusual biology of aliens. In the films, the details of a species are rarely gone into in any depth.
    • A bit of Bizarre Alien Psychology: Thakwaash, a horse-headed species of humanoids, easily and healthily form multiple personalities, to the point that they are "We" and not "I". Runt from the X-Wing Series washed out into Wraith Squadron because his incoherent, borderline suicidal "pilot mind" wouldn't obey orders and in simulators tended to get killed.
    • Twi'leks, those very humanlike aliens with odd-colored pigmentation and a pair of braintails instead of hair. The braintails are mobile enough that they are used in a low-grade Starfish Language (in practice, they use them in conjunction with spoken language, adding nuances that humans and other species that lack such appendages are incapable of replicating) and in some adaptations seem to be prehensile, and they actually do have some brain tissue in them. Aayla Secura, after going completely amnesiac thanks to a Dark Jedi, has her memory restored later when someone does something to her braintails. Twi'leks can survive losing part or all of a braintail, but this is really painful and depending on how much is lost, is like a lobotomy.
    • Galaxy of Fear: Eaten Alive has Enzeen, blue-skinned humanoids with spikes for hair, which seem like perfectly respectable Rubber-Forehead Aliens... but are actually symbiote/parasites there to attract offworld visitors who are then eaten by the planet. The Enzeen feed by thrusting their hollow tongues into the soil where people have died and sucking nutrients up. It's speculated that they didn't evolve like that but were designed for this purpose.
  • In Stay Out of the Basement, the main character's dad is replaced by a Plant Person who looks exactly like him on the outside (even more so once the original grows leaves in place of hair), but bleeds green blood. When he's killed at the end, he doesn't have any recognizable human organs inside.
  • Inverted in A Strange and Ancient Name, in which iron is deadly to elves and the tiniest scratch means certain doom. When the half-human prince gets stabbed by an iron weapon, the kingdom goes into mourning, waiting out his long and painful death. Until the (human) love interest points out in a rage that maybe his despised heritage makes him less susceptible to the effect, and the healers decide to actually try to help him.
  • "Saul's Death: two sestinas" is a Rhysling-Award-winning poem by Joe Haldeman.note  Narrated by an unnamed human fighter, it tells the story of his life as a mercenary and his friendship with another mercenary, named Saul. It concludes with the twin revelations that Saul looks human but has vitals "like nothing in this world," and the narrator is a time traveler from the future.
  • In Zenna Henderson's short story "Subcommittee", Earth is invaded by fuzzy, brightly hued Humanoid Aliens. After a huge war in space, representatives from each side begin peace talks. The humans are appalled when the aliens appear to be asking for all of Earth's oceans. Naturally, it's the wives of two of the chief negotiators, plus their adorable sons, who discover the truth that leads to peace. It turns out that the aliens have become infertile due to lack of a vital nutrient... which is revealed to be salt.
  • The Pack and Ontongard (as well as the titular character) from the Ukiah Oregon series look human to all casual inspections, but the fact that their spilled blood/removed flesh turns into animals and runs away kind of gives the game away to any kind of medical inspection.

    Live-Action TV 
  • As the only alien species on Alien Nation, the internal parts and biochemistry of the Newcomers are well-documented and used in the story for humor and drama. Some notables:
    • Survival in hazardous environments.
    • Great physical strength.
    • Nerve plexus under the arm; their most sensitive area, a key pressure point in a deadly Overseer martial art.
      • Regular humans have a fairly major nerve cluster in the same place. Although attacking one won't kill, it can do some damage.
    • Males receive half-formed infants from their mates for further development, like a cross between a marsupial mammal and a seahorse. (George Francisco was the first male TV character to give birth on-screen.) Conceiving said infant requires all three sexes to participate, by the way.
    • They become intoxicated from spoiled milk.
    • They cannot digest cooked animal proteins, and subsist on raw meats.
    • Saline water dissolves their flesh like acid.
    • Two redundant hearts; they can take a huge bullet in one of them and not stop attacking.
    • A frightening, monstrous metamorphosis triggered by an overdose of a unique narcotic.
    • A gland in their neck when implanted into a human inhibits the human aging process (but its removal kills the newcomer). Information buried to prevent genocide in the quest for eternal youth.
  • Krevlornswath ("Lorne") of the Deathwok Clan of Pylea on Angel looks quite humanoid, other than the green skin/red eyes/horns thing. You figure out they're called the "Deathwok Clan" for a reason when Lorne gets beheaded and remains alive as long as his body isn't destroyed.
    • Lorne's hulking, bearded mom.
      Lorne: I thought Our Lady of the Perpetual Seabreeze was the real deal, till the Divine Miss J. walked right through that door and into my ass ... which is where my heart is. Physiologically. I could show you an X-ray.
  • The Centauri on Babylon 5 look enough like humans that they were able to briefly fool Earthers into thinking that they were two branches of the same species. However, among their known physiological differences are a lack of major veins/arteries in their wrists, two hearts, and radically different sex organs: males have six two-meter-long prehensile genitalia located on either side of the back, and which curl up under the arms when not in use, while females have six corresponding orifices. Consequently, Centauri can rate how far they've gotten from "one" to "six". They are, however, also seen kissing human-style.
    • According to the first Psi-Corps Trilogy novel, most humans of any importance were highly skeptical of the claim, and performed genetic analysis as soon as they could get a hold of some Centauri tissue.
    • In one episode, Londo mentions that he once caught the emperor (back when he was an adolescent) trying to peek up women's skirts. A fan commented that from what we've been told about Centauri biology, he was looking in the wrong place. JMS responded "tell that to a foot fetishist."
    • Male Drazi have a 'pouch' situated in their left armpit. It is clarified to be their reproductive organ.
    • Narns are marsupials. 'Pouchling' is an insult when applied to an adult. And MALES have the pouch!
    • Minbari, being from a planet that's much colder on average than Earth, also have a much lower tolerance of high temperatures than humans.
      • Their bone density is higher than humans (and not just the part that protrudes from their skulls), giving them more strength. They're also able to stand more physical trauma, as evidenced when Delenn was nearly bled out, and Franklin commented that if a Human had lost that much blood, he'd be dead. Alcohol causes them to fly into homicidal rages. And this might not be Canon, but it's been stated that Minbari have a weak sense of taste, and as a result their food is all very spicy.
      • In the episode where John cooks Delenn some Minbari food (that looks like cubes of tofu); Delenn hastily seasons her meal when John isn't looking. Supposedly this is because he prepared it too blandly. Or he's just a lousy cook (which he admits), and she tries to cover the unappetizing taste with spices.
      • In one episode; Vir describes being sick after eating Minbari food. He remarks on the strong and good flavor as why he risked it. But if that is describing Minbari taste; Centauri taste; or both is never explained.
    • Pak'ma'ra are carrion eaters, with prehensile Cthulhu-esque tentacles on their faces used for drawing in food. Under the tentacles is a beak, and they require translators to speak to other races. Also, according to the doctor in Crusade, they are not sexually compatible with humans.
  • One of the few alien aliens to appear of Blake's 7 did a very good job of imitating humans, but reverted back to their original form after being shot. Well, mangled original form, due to being shot and all. Because of this, they could have a definitely non-human thing lying on the floor, oozing goo and gurgling without needing to be able to fit an actor inside.
  • Doctor Who:
    • Time Lords have two hearts with a redundant circulatory system, a low body temperature, a respiratory bypass system, an ability to regenerate from death twelve times, a lifespan of potentially hundreds of years per body, and a complete additional sensorium tuned to temporal events. The show never addressed how the Coal Hill School nurse failed to notice that Susan was not human.
    • In "The Dominators", the Dominators scan the Doctor's companion believing him to be a native of the Alien Planet of the Week. A later scan of an actual native reveals a totally different anatomy, which backs up the Doctor's earlier lie that there are two intelligent species on the planet.
    • In "The Dæmons", the Doctor claims that an aspirin might kill him, though it's not clear whether he actually means it, or is just contriving a possible example of why human medical advice does not apply to him.
      • And even assuming he was telling the truth about his reaction to aspirin, it's not clear if this is true for all Time Lords, or if it's just that the Doctor is severely allergic to it.
      • In an earlier episode, the Doctor mutters about his different biochemistry to avoid being injected with an antibiotic cocktail by Liz Shaw, who promptly overrules him. He doesn't suffer any apparent ill effects.
    • This trope is directly mentioned in "Genesis of the Daleks". A Kaled scientists scoffs at the Doctor and his companion's claim that they're not from the planet Skaro. Then their test results come back, leaving the scientist stunned that, despite external appearances, their biology matches nothing native to Skaro.
    • Kaleds themselves looked like dark-haired, dark-eyed humans on the outside. However, they had fewer ribs than humans in a more widely spaced ribcage, greenish copper-based blood, purple body tissue, thick lungs, and grey cardiac muscle.
    • The very rare inversion did happen once: in "The Hand of Fear", Sarah Jane shakes off a "lethal" poison, as it turns out not to be lethal to Homo sapiens.
    • The Fifth Doctor claims that he wears the celery because it's an excellent restorative. He also claims that it will turn purple in the presence of certain gasses that are toxic to him.
      • The Eleventh Doctor asks for celery after a Silurian disinfection attempt.
    • In the Movie, the Seventh Doctor is shot three times in total, in the shoulder and the leg; dialogue makes it clear that these were not fatal wounds. The issue is that the medical team don't understand the Doctor's alien biology, think he's fibrillating wildly out of control due to his (for a human) incredibly high pulse rate of 300 beats per minute, and place a surgical probe in his circulatory system to try to find out why. Unfamiliar with the circulatory system of an alien with two hearts, the probe gets lost, damages the Doctor's body, causes him to have a seizure, and the doctors' panicked attempts to remove the lost probe and revive the Doctor kill him. The Doctor's regenerative process is inhibited by the anaesthetic for several hours (the Doctor himself conjectures that this is why he has amnesia for several more hours following his regeneration), and the scene in the operating theatre makes it clear that the medical staff are also surprised by how much anaesthetic it took to knock the Doctor unconscious.
    • In "The Unicorn and the Wasp", the Doctor recovers from cyanide poisoning by ingesting a variety of different ingredients and shocking himself — the biological Techno Babble was actually vaguely in the right area for curing cyanide poisoning. "Smith and Jones" also has him survive radiation poisoning from an X-ray by expelling it all through his foot. He also states that Time Lords are immune to most forms of ionizing radiation and he used to play with Roentgen bricks in his nursery.
    • When the Tenth Doctor regenerates into the Eleventh, the regeneration causes some sort of biochemical imbalance that the Doctor is trying to counteract by eating various foods. Finally fish fingers dipped in custard do the trick.
    • In "Cold Blood", a Silurian attempts to subject the Doctor to a procedure meant to remove surface bacteria that are indifferent to humans but potentially dangerous to their colony. The Doctor suffers considerable pain from the process, and would have died if it weren't called off.
    • Humans who spend a lot of time exposed to time travel acquire immunities to certain time travel phenomena. There is an implication that the Doctor's companions are slightly "changed" after travelling through time due to being exposed to the energies of the TARDIS. An episode of Torchwood showed that Martha's white blood cells, and who knows what else, had been slightly mutated.
      • The Dalek in "Dalek" apparently specifically needed DNA from a time traveller in order to regenerate itself (and its casing), implying that time travel does something to DNA that makes it categorically different.
    • "A Good Man Goes to War": Amy's daughter, Melody Pond, aka River Song, became half-Time Lord with the ability to regenerate as a result of being conceived inside the Time Vortex.
  • There are several near- and full-inversions in Farscape: humans are far less sensitive to heat than the outwardly-similar Sebaceans, allowing them to survive in warmer temperatures. On the other hand, all of the alien races have much better eyesight — though this too once proves to be an advantage to Crichton, as it renders him less susceptible to a mind-altering cosmic lightshow. Sebaceans also have a good number of internal differences like the lack of kidneys despite the fact that Sebaceans might be related to humans and a smoother pregnancy.
    • Farscape is the only series in which humans are not the Jack of All Stats.
    • Each race has its own differences; in one episode dealing with excessive radiation in Moya, Chiana talks about how she's got a heightened resistance to it, while Sikozu talks about how limited exposure would make a good number of her vital organs shut down.
    • Delvians are plants and get sexually aroused by intense light.
  • Intergalactic: Candy is a woman from the Aurean galaxy. Her species looks outwardly like humans, though with long, prehensile forked tongues, as she displays early on.
  • In Mork & Mindy, Orkans can drink with their finger (and use various Psychic Powers focused through their index fingers), have three hearts, physically age backwards, and hatch from eggs which come from the male's bellybutton. And according to the pilot episode, their "parts" are interchangeable. In the season 2 opener, Mork takes some medicine designed to shrink nasal membranes, then says that Orkans are all membrane and shrinks down to the scale of an Earth-like nano-world.
  • My Hero (2000) did a fair number of jokes revolving around the quirks of Ultronian anatomy, ranging from "unpleasant reactions to everyday chemicals" to "blue urine" to "unpredictable bouts of coma".
    • The "unpredictable bouts of coma" being a result of a dodgy heart that would stop and start irregularly. Easily fixed (on Ultron, that is), but the coma that occurs when it stops is indistinguishable from death by human technology...except that some time later it restarts and the Ultonian just wakes up like nothing happened.
  • Red Dwarf:
    • In an early episode of the series (which, in fact, is entirely devoid of actual aliens):
      Rimmer: Lister, just because they're aliens, doesn't mean they don't have to go to the little boy's room. Of course, they probably do something weird and alien-esque, like it comes out the top of their head, or something.
      Lister: Well, I wouldn't wanna sit behind one in a cinema!
    • Despite the Cat appearing to be mostly humanoid aside from his obvious feline teeth, he is said to have six nipples, colour-coded organs, and his heartbeat performs its own rumba, making it "much cooler" than a human's.
    • Also inverted in the episode "D.N.A.". The crew encounter a three-headed, very alien-looking corpse, but said corpse has a wallet containing credit cards and a video club membership card. The corpse is a human who over-used a machine that messes with the subject's DNA while — somehow — leaving the mind and personality intact. So Alien Outside, Human Inside.
  • In Roswell, Max gets drunk with just a "little sip" of an alcoholic beverage in about two seconds, and gets back to his sober self without a memory of what he did, or any apparent hangover once he kisses Liz (or might have just been a coincidence). Michael, on the other hand, didn't get drunk the same way, but he got a sort of allergic reaction which made him have electrical lines running through his body, and every sense in overdrive. He did have a hangover. And although their biology is rather human except for their cells, it is said they can sustain a one hour climax, even if they don't go into details about how that exactly happens...
  • The Mage Species from Sabrina the Teenage Witch have some incredibly bizarre biological quirks, far beyond what their magical powers would imply. Possessing certain character flaws can inflict them Anvilicious pun-based mutations (for example, a witch who acts "spoiled" will start to dissolve into foul-smelling ooze), their magic needs to be extracted and "tuned up" regularly to function properly, and their wedding vows involve exchanging ring fingers.
  • On the short-lived NBC series Something is Out There, the alien Ta'ra has a number of physiological differences: caffeine was an inebriant, and hands were apparently primary erogenous zones. Additionally, she felt the need to sleep in the nude and at one point became sexually aroused watching Crime Story. The latter two may have been more cultural than physiological, however.
  • Most of the aliens in the Stargate-verse are Transplanted Humans, so they rarely fit this trope, but there are a few aliens that definitely do.
    • Jaffa were genetically engineered from humans as a slave race by the Goa'uld. A Jaffa's lifespan is about 150 years or so and they have a symbiotic relationship with young Goa'uld that lives in a pouch in their belly and provides them with a supercharged immune system and great physical strength. If deprived of a symbiote or a medication that simulates its effects, a Jaffa will die in hours.
    • The Wraith are both insectoid and vampiric. Physically they look like Rubber-Forehead Aliens, but their humanlike digestive system is vestigial. Instead, they feed on the life energy of humans through mouths on their hands, and when well-fed they are extremely strong, fast and tough. Their society resembles an ant colony, with a ruling queen and many subservient drones under her. They are apparently (somehow) evolved from the insect-like Iratus bug, which similarly feeds on the life force of its victims; apparently feeding consistently on humans for a long enough time caused some of the bugs to become humanlike themselves, gaining human intelligence but with the side effect that the Wraith can only feed on humans (or other Wraith).
    • The unnamednote  species to whom Bounty Hunter Aris Boch belongs (Stargate SG-1: "Deadman Switch") looks completely human. However, their blood is yellowish green, and something about their physiology makes them immune to Goa'uld infestation.
  • Star Trek likes doing this. A typical Vulcan has a much larger "nonhydraulic" heart located where a human has his liver, copper-based green blood (based on hemocyanin, the copper-based blue-green blood found in a number of real world mollusks and arthropods), nictating membranes in his eyes, a body temperature over 105 degrees Fahrenheit, and a standing pulse rate of over 200. And Pon Farr as well. Klingons have evolved truly complex redundant biologies, making them next to invulnerable, though prone to many minor malfunctions. They also have thick, pink blood, though we have seen otherwise, including in the theatrical version of Star Trek VI, which introduced the idea (video releases restored a scene showing that the red-blooded Klingon was really a human wearing a mask). There are certainly others.
    • The Trill are (two or) three species with separate degrees of this. The Trill symbionts are alien slugs that live for millennia. The humanoid Trill are, conveniently, fitted with a womb-like pouch inside the body that can bond with the symbiont Trill. When bonded, a Trill composed of a symbiont and a humanoid host now have one mind and one personality, to the extent that they are legally a brand new species. How the two species ever figured out that this could be done (it's not exactly the most obvious thing you'd think to do when meeting another intelligent life form) is unclear.
    • Betazoids, despite looking entirely human (apart from their black irises), have an extra lobe in their brain to account for their telepathy.
    • The Denobulans have a distinct mating season (when the males fight for mates) and hibernation period. They also can puff up their heads like blowfish to scare predators.
      • Phlox's bizarre biology was an ongoing joke in the series. He has striped toenails that grow so rapidly they have to be cut once a week, a 16-inch tongue that needs regular scraping and a smile that the Joker would envy. Plus he hibernates five to six days a year.
      • Rajiin is an Oran'takun with the ability to do a complete biometric scan of someone, then wipe their memory of the event, though it's possible some of these abilities have been surgically implanted.
      • The episode "Two Days & Two Nights" brought us the second encounter with shape shifting aliens:
        Trip: You think this is my fault?!
        Malcolm: You were willing to follow two strange aliens into a basement.
        Trip: Gorgeous aliens! Don't forget they were gorgeous.
        Malcolm: They were male!
        Trip: Not at first!!!
    • In the Star Trek: Voyager episode "The Disease", Harry Kim has sex with a woman who looks human (as mentioned in the title quote) but prolonged sexual contact makes his skin glow, as well as making the two become physically addicted to each other.
    • Pregnant Bajorans have sneezing fits instead of morning sickness. And a complex network of veins bonds the mother to the child, which was the reason for why Nerys couldn't give the embryo back to Keiko (It Makes Sense in Context).
    • The freaking Ocampa. Lifespan of nine years. Body temperature around 16 degrees Celsius. Can only have one child. When ready to mate, they exude a yellow substance from their hands and must have an hour long foot massage with 50 hours of the substance appearing to enable mating. Give birth standing up, from a sack between their shoulders. While their psychic powers probably helped, one still wonders how a species with such a bizarre, and mathematically troublesome, method of reproduction could have come about in the first place.
    • A Starfleet officer on DS9 named Vilix'pran (whose species has not been shown on screen) "budded" many children. Who had wings that had to be kept from tangling. Oh right, Vilix'pran takes the pronoun "he".
    • When Quark and his family were accidentally sent to 1947 Roswell, we learned that Ferengi biochemistry is sufficiently different from our own that sodium pentathol injections do nothing besides making them very sore at the injection site. Ferengi also have four-lobed brains, which somehow makes them immune to telepathy.
    • This is done with humans in the episode 'The Communicator' when Archer and Reed are captured on a pre-warp planet who initially think they are spies; when medically examined, the aliens comment on their "redundant renal organ" and "red blood with haemoglobin based on iron, a toxic element" and that they are missing four vertebrae. However, their captors assume that Archer and Reed are genetically engineered Super Soldiers rather than aliens.
      • It also helped expose Riker in 'First Contact' (the episode). Alien doctors examining an unconscious Riker are surprised to find his heart where his digestive tract should be, among other things.
    • Ash Tyler from Star Trek: Discovery is a bizarre case. He looks perfectly human, and even has human organs, albeit with unusual scarring. As it turns out, he's actually a Klingon named Voq who was physically transformed into a human, complete with internal organs harvested from the real Ash Tyler. He even has a human personality overlaid atop his Klingon self, the latter of which can be reawakened with a Trigger Phrase. He is epically freaked out when he learns the truth about himself.
    • Adira Tal is literally human on the outside and alien on the inside: they're a regular human from Earth, but they're hosting a Trill symbiont, implanted in an emergency so it could survive.
  • There is only one known alien race in Time Trax, and they are shown and mentioned in only one episode. The Procardians appear to be your usual Human Aliens without any extenal differences, but have a number of biological oddities about them. They can glow and levitate like the aliens in Cocoon. Their voices sound very odd to the point where their vocal cords are incapable of producing human speech (and vice versa), although one attempts to say "Thank you" at one point and it sounds a little like Helen Keller. They age in stages, meaning they can look exactly the same for several years before metamorphosing into an older equivalent. Since the change is so sudden, it can be difficult to recognize the same Procardian after one such change. Another bizarre feature is their equivalent to our fight-or-flight response to threat. They raise their arms in a combat-like stance, which fires an energy bolt at the threat. The effect of the bolt (on human, at least) is a coma-like state, which can be "cured" with shock therapy. This reaction is instinctive, as they have no adrenalin. Oh yeah, they also don't wear clothes.
  • The Twilight Zone (1959): In "The Fugitive", Ben belongs to a race of shapeshifters but their default form is entirely human.

    Myths & Religion 
  • Many creatures in old folklore have odd habits and biology. For instance, faeries were vulnerable to iron (particularly worked iron). In some stories of vampires, they could not resist counting things such as scattered poppy seeds on the floor.

  • In the Big Finish Doctor Who Companion Chronicle "The Darkening Eye", Adric survives a stab wound to the chest because of his species' Healing Factor and the key little detail that his assailant was aiming for the location of a human heart. Guess which side of the chest cavity holds an Alzarian heart?

    Tabletop Games 
  • Warhammer 40,000:
    • The Space Marines superficially resemble oversized humans, but that's where the resemblance ends, as the process that turns them into Marines involves surgical insertions of multiple extra organs, restructuring of their skeletons, and more. Among others, they have two hearts, a third lung, organs that let them access memories from flesh of others, a membrane enabling them to enter suspended animation, near-total immunity to non-Chaos poisons and illnesses (they can actually store poison and use it later), ribcage remoulded into ribbox and "second skin" under normal one that doubles as light armour and enables controlling their Power Armour with their mind. They're also capable of breathing water to some extent and their lungs can filter air so that they can walk through sandstorm and be barely affected, not to mention that all of their senses are greatly improved.
    • Eldar are also a lot more inhuman than their appearance would suggest. Physically they look like tall pointy-eared humans with almond-shaped eyes, but their musculature is somewhat different (making them stronger than their lithe appearance might suggest), their reflexes are far superior to human ones, and they experience emotions far more strongly than humans do. Eldar pregnancy also lasts much longer than humans (exact length is not mentioned, but it's implied to be several years). According to Xenology (a background book which contains reports of autopsies of several different alien specimens, written from an in-universe point of view), Eldar internal organs also differ from human ones, their skeleton is of entirely different composition (being more flexible and plastic-like than human bones), their droppings are crystalline, they have no conventional teeth but instead have serrated pieces of jawbone not unlike some species of birds, and their DNA is composed of two entwining double helixes. Also, their ears may be erogenous zones.
  • Invoked in Werewolf: The Apocalypse, with the Ananasi were-spiders. The splatbook mentions that while they look outwardly human, their internal organs are nothing of the sort, instead being a blend of human and spider organs.

    Video Games 
  • No matter the race of the Dragonborn from The Elder Scrolls V: Skyrim, everything about them on a metaphysical level is a fire breathing, flying lizard. This allows them to pull off feats that horrify mortal and dragon alike.
  • EXTRAPOWER: Some of the alien characters look indistinguishable from humans, apart from maybe the green skin of the Shakun people. Typically the biological differences never come up, but it becomes a dramatic point in Attack of Darkforce when Daitoku Igor needs to have a mind control device surgically removed from his head. With the medical staff that the SPICA mercenary group has on hand, it'd be easy enough if he were human. But as a human-looking alien, they don't know enough about his biology to be able to safely begin operating.
  • The asari in Mass Effect can mate with anything that has DNA to produce viable offspring. The actual mechanism is parthenogenesis coupled with the ability to scan DNA via biotics, plagiarise useful segments, and modify the genome of their offspring. Physical mating is optional.
    • For asari, mating within their own species can result in severe, highly dangerous genetic defects down the line in a manner loosely akin to incest. That's about as bizarre as biology gets.
      • This is far more rare than their cultural taboos would suggest. And it's a good thing since "pureblood" asari (an asari born with two asari as her parents) is more likely to be or give birth to an Ardat-Yakshi (a asari with a rare genetical disease that makes her become a sex-addicted murderous sociopath over time and causes death to her partners by frying their neural system). A textbook example is Samara, who is a "sane" pureblood and gave birth to three pureblood and Ardat-Yakshi daughters).
    • Pursuing any Interspecies Romance in ME 2 brings this subject up — many alien races are humanoid, and a few are even primate-like mammals, but beyond that, all bets are off to the extent that the ship's resident scientist, a specialist in genetics and xenobiology, can give the player character medical advice concerning the physical... difficulties... such a relationship entails. Gets really uncomfortable when you realize that two of the romance options are a reptile and a (flightless) armor-plated bird/dinosaur, albeit humanoid...
      • While quarians seem to be mammalian and more or less human in appearance (it's hard to determine through the enviro-suits they need to wear to ward off infection, and it's implied they don't have ears like a human — and they have only three fingers to either hand), they share the unique trait with turians that they are made from "dextro-amino acids". And No Biochemical Barriers is most definitely not in effect in the Mass Effect universe: anaphylactic shock is a very real possibility. In fact, talking to the doctor while pursuing the female human/male turian relationship has him discretely recommend "avoid ingestion".
      • Oh, and the aforementioned reptile alien romance? Sustained skin contact can cause rashes in humans, and humans who make oral contact with them can likewise experience hallucinations.
  • Samus Aran, despite having been infused with DNA from two different alien races, still looks like a perfectly normal human being.
  • In World of Warcraft, draenei have blue blood (confirmed both in-game and in tie-in novels), which implies rather exotic biochemistry. And yet, they can interbreed with orcs, who didn't even originate on the same world...and then, a hybrid of the two proceeded to have a child with a human. Go figure.
  • Sims aren't aliens, but they aren't humans. They age rather quickly, have short lifespans, apparently have clear urine, and vomit pink no matter what.
  • Inverted in Sam & Max: Freelance Police, Dr. Norrington said that The Great Old Ones are identical to humans, and by extension animal life on the inside. "We save the weird stuff for the outside".
  • Teddie of Persona 4 is a sentient Shadow who purposefully crafted a human body to interact with the main characters in the real world. Naoto has Teddie undergo a few medical exams, and discovers that the X-ray turned up completely blank.

  • In Freefall, Sam Starfall looks like a normal if not-quite-human humanoid. Turns out his head is a special type of space helmet, and from inside he can control the expression pretty extensively. This is why he never needs a helmet even when Florence, a genetically-engineered humanoid wolf, requires one. His entire suit is implied to work similarly. His actual appearance involves lots of tentacles.
  • Schlock Mercenary has many species that qualify for this trope, looking generally human while explicitly not actually human. Author Howard Tayler loves to describe the details in footnotes for the strip. One of the more obvious examples among the regular cast is Lt. Ebbirnoth, who has one large eyeball where one would find a head on a human. This becomes a plot point during the first Credomar story, where a human sniper targets this eyeball thinking that doing so would actually damage the brain, which for Ebby's race, called Uniocs, is actually located in their pelvis.
  • In El Goonish Shive, the Uryuom are sexless; they produce "eggs" which can accept and combine DNA from multiple individuals, even those of different species ("the current record is twelve parents, only nine of whom were Uryuoms"), Uryuom DNA need not even be part of the mix. They have limited shapeshifting powers and use limited telepathy to have a common language with anyone in three seconds or so and instead of pheromones. They also have advanced shapeshifting technology that lets them not only mimic another race's outer appearances but also become biologically compatible.
  • In Drowtales, the Fae (drow, light elves, drowussu etc) are more biologically different than their humanoid appearance would suggest. They key to this is mana; the energy they generate, absorb and manipulate. It is the source behind their comparative resistance to, and lack of, diseases (they are not completely immune though). It is also what keeps them young and in a healthy condition, provided there are enough of them to generate a surplus of mana. Young drow age about half the rate of humans physically, but only lag behind 2 years mentally (a drow who is 30 would look 15 physically but be about 28 mentally). If they live with enough other fae they will stop aging at about 60 (the equivalent of a 30-year old human). They still need to eat and drink, but less so than a human of comparative size would and their bodies does not store fat they way a human body does. Their nature means that they also can "starve" even when they have plenty of food and drink - if they are alone. If that happens they will start to suffer from mana deprivation and starts to age much like a human would. They also get high on chocolate and the like.
  • Happens a few times with Aylee in Sluggy Freelance, though it's usually overshadowed by her more overtly alien features. When she first arrives on Earth, she has a hard time remembering that humans need to sleep and breathe occasionally. During one of her transformations, she also develops an entirely potato-based diet.
  • Played with in Penny Arcade, in reference to Mass Effect.
  • A similar example is this The Perry Bible Fellowship comic.
  • Similarly, in The Order of the Stick, it's offhandedly mentioned that a dwarf died from alcohol poisoning when "both his livers" gave out.
  • Homestuck:
    • The trolls look like humans with gray skin and horns, but references are made them having insect-like physiology, and young trolls look like grubs. Individuals can have blood of almost any color of the rainbow (in fact, blood color is the basis of their caste system). We're not given much detail about their reproduction, but the act involves filling pails with genetic material—and individual trolls are required to fill pails with two different partners: a pairing based on mutual love and a pairing based on mutual hate. Troll biology sure is weird!
    • The cherubs look like humans with forest green skin, no hair and weird cheek protrusions with spirals on them, which is still within the bounds of what can be cosplayed, but are even weirder than the trolls. All of them are born with two distinct Split Personalities, which are indicated by the color of the spirals changing, and eventually are supposed to mature via a Split-Personality Merge, which will change the spirals to circles. Their relationships are exclusively based on mutual hate, and when reproducing, they transform into cosmic, indestructible snakes.
  • Chainsaw Suit demonstrates some... side effects.
  • Eiffel, the alien in Fall City Blues, looks human but eats rocks.
  • The title character of Selkie has some odd dietary requirements and needs to wash her gills out regularly. She's also apparently ectothermic, despite the author stating that adult females of her species have mammary glands. The fans have gotten up in arms trying to figure her out.note 
  • ALL aliens in The Accidental Space Spy have this. In lesser extent the author's other webcomics.
  • In The Inexplicable Adventures of Bob! Princess Voluptua is an Insectoid Alien who disguises herself as a human; but even in insect form, she appears to have Non-Mammal Mammaries. It turns out they're ovipositors. She had assumed that that's what they were on humans, too.
    Jean: Do you even know what a mammal is?
  • Gunnerkrigg Court: Jones... probably. Strictly speaking, no one knows what her insides consist of because she's so completely over-the-top indestructible that even X-rays just bounce right off her. She doesn't eat or sleep or age, so whatever's going on in there clearly doesn't resemble Earth biology, even though she looks like a normal human from the outside.
  • Sam & Fuzzy: Vampires, and possibly some of the other inhumans.
    Edwin: [after getting stabbed] It's... It's ok... Vampire biology... different from human. Heart and lungs... actually in head.
    Devahi: What's in your chest?
    Edwin: 17 appendixes. Should be fine. Only need 11.

    Web Originals 

    Western Animation 
  • In Ben 10, Osmosians look externally like humans, but have the ability to absorb matter and energy, as well as minor degrees of super-strength and durability, which increases when they do. Though to them, pure energy is a G-Rated Drug that drives them insane if they absorb too much of it (though this is reversed if the energy is discharged). Also, Osmosians can live much longer than humans and those who live for hundreds of years grow horns. Of course, to be fair, in Omniverse, we find out that "Osmosians" look as human as they do because they are humans, just mutated a bit, and Aggregor, the only member of the "species" to have horns, was artificially created.
  • In Invader Zim, despite the fact that Zim can pass as human with only a minimal disguise (though that's really more due to how stupid humans are) it's implied that Irkens have none of the same internal organs as human beings. They do, however, possess a master organ called a squeedlyspooch around where humans have stomachs.note  The episode "Dark Harvest" revolves around this: Zim, in an effort to perfect his human disguise, crams his body full of stolen organs, including six hearts and spleens in three different colors. Irkens (or perhaps just Zim) also have allergies to some very common items... like water (possibly just polluted water), meat, and barbecue sauce.
  • Most aliens in Men in Black: The Series are Starfish Aliens, but Jeeb's unnamed species is identical to humans in every aspect other than their ability to regenerate any wound including the destruction of the head, so long as they have oxygen.
  • The Owl House: "The Intruder" reveals that aside from having pointed ears, witches also differ from humans by having a "bile sac" attached to their heart that lets them channel magical power. "Separate Tides" also reveals that a lot of their food is undigestable for humans.
  • The inhabitants of Mewni from Star vs. the Forces of Evil are beings from Another Dimension who look identical to humans from the outside, save for females of the royal family having Blush Stickers with unusual shapes (for example, main protagonist Star's are heart-shaped and her mother's are diamond-shaped) which sometimes change to other shapes according to their emotion. Female (it's unknown if it's also the case for males) teenagers will go through a variant of puberty called "Mewberty", which causes them to become boy-crazy and eventually turn into purple-skinned moth people who will attempt to abduct any boy in sight until it passes, at which point they will return to their original form with only small wings as a reminder of the event. Men (a few of whom have been seen shirtless to confirm this) lack the wings. One of them survived decapitation and even had his severed head implanted on the neck of a horse with no apparent problems, but that might have involved magic.
  • Steven Universe: The Gems are an extreme case of this. Aside from skin, hair, and body colors based on their namesake jewel and a gemstone sticking out of part of their body, they would look perfectly human, with only a few having more nonhuman features. However, the only real part of their body is their Gem- every other part of them is simply a Hard Light hologram created for the sake of interacting and walking around. They don't physically age, can mix their projected forms together with other members of their species, and don't need to eat, breathe, or sleep. Temperature also fails to affect them outside of extremes — and even then, certain individuals can swim in lava. If their body projection gets too severely damaged, they will simply retreat to their gem and reform later, only a crack in their gem can seriously incapacitate their projected form, but it can easily be healed by Steven and Rose, and the only thing that actually comes close to killing a gem is to shatter them, and even then, their gem shards can still form as incomplete, mindless body parts. Also played with, as the Crystal Gems deliberately made their bodies so internally human-like as to include organs that they don't actually need (otherwise they appear to have no internal organs at all).
  • Inverted in Teenage Mutant Ninja Turtles (2003). Baxter Stockman and Oroku Saki a.k.a. The Shredder see a thermal camera image of the Turtles, which looks roughly like a human being's heat signature — only humanoid-turtle shaped. They also sweat. This implies that they have a human-like metabolism. They seem to be Turtle Outside, Human Inside. They also have a full set of teeth, and eat human foods. If you have a turtle, don't give it pizza or Chinese food unless it too is a humanoid mutant — it's not good for them.
  • Starfire from Teen Titans (2003). Aside from her decidedly orange skin and her ability to fly and to shoot energy from her hands and eyes, she has nine separate stomachs, an oft-unused long, prehensile tongue, a temporary but extensive Metamorphosis triggered by puberty, and a nasty allergy to metallic chromium.note