When characters are mistaken for the beings of another world. If you travel through time (especially to the mid-20th century or thereabouts) or are an astronaut, this will probably happen to you at least once.
Yet another variant of Mistaken for Index. For aliens not from space, see Mistaken Nationality. For magical beings mistaken for aliens, or vice-versa, see Alien Fair Folk. Often overlaps with Human All Along.
- One episode of Ouran High School Host Club had Honey's younger brother Yasuchika accuse him of being an alien simply because he eats three cakes at once in less than a second once a week.
- Franken Fran helps an actress who has fallen for a male lead who is obsessed with anime features, and wants to star opposite him in live-action adaptations. She insists on ever more extensive surgery but fails to take Fran's advice at the hazards in her rush to bed the actor, and cosmetically falls to pieces. He flees in terror, then goes on so many talk shows raving about Grays trying to abduct him that he doesn't get any more roles.
- A running gag in Squid Girl - Cindy Campbell and her colleagues are convinced that Ika Musume is from outer space, and they would very much like her to visit their laboratory.
- Parasyte: The Japanese government assumes that Hoshikawa is a Parasite, but after they shoot him discover that he was Human All Along, and is just a Misanthrope Supreme who honestly believes in Parasite supremacy.
- Lamput: In "Alien Again", Slim Doc is blue-gray and wears white clothes just like the extraterrestrial visitors. One of those visitors immediately thinks Slim is one of their group, leading to him being trapped in their spaceship.
- Motu Patlu: In "Alien Patlu", Dr. Jhatka gives Patlu an injection that gives him extra eyes, which are on eyestalks on both sides of his head. The eyestalks resemble alien antennae, causing people, and eventually actual aliens, to mistake Patlu for an alien.
- The Teenage Mutant Ninja Turtles do this on purpose in the third Mirage comics volume; aliens having openly made contact with Earth, it's apparently easier for people to accept that than homemade mutant freaks.
- Cracked had a 3rd Rock from the Sun parody in which aliens mistake the disguised alien family for real humans.
- The Boy Who Cried Idiot: When Lincoln screams, Martin thinks he's an alien.
- The sixth edition of Halloween Unspectacular has a story wherein Gaz is abducted by government agents who have come to the conclusion that she's an alien. They proceed to torture her for information that confirms all their theories, and then almost dissect her alive before they realize their mistake. It then turns out that Zim deliberately tipped off the agents about Gaz, hoping they'd kill her, just because he knew it'd upset Dib.
- Invoked near the end of the Invader Zim fic Motivation. Desperate to capture a recently Heel-Face Turned Zim, Agent Spider abducts Dib and uses circumstantial evidence to present him as an alien, which all of Spider's colleagues are completely fooled by. Dib ends up scheduled for an Alien Autopsy by the coldly indifferent government scientists, with Spider counting on Zim intervening to save Dib and thus expose himself.
- Inverted in Wander over Foster's AU One-Shot. Wander is an alien from another planet, but everyone but Bloo believes he's just a traumatized Imaginary Friend who thinks he's an alien.
- In Back to the Future, the DeLorean Time Machine was mistaken for a UFO in 1955 due to its gull-wing doors. The fact that Marty was wearing a radiation suit at the time didn't help. He turns it to his advantage later, when he orders his father to hook up with his mother.
- Grand Fenwick's chainmail-clad longbowmen successfully invade 1950s New York City in The Mouse That Roared because of being mistaken for Martians.
- In Go to Mars, Abbott and Costello land an experimental rocket ship in New Orleans, and the locals' large papier-mâché Mardi Gras costumes convince them that they've landed on Mars.
- Played for Laughs in The Avengers (2012) where Bruce Banner as the Hulk falls on a warehouse, half-destroys it and becomes human again. There, he speaks to an old man, a security guard, who believes Bruce is some sort of alien. The security guard is played by Harry Dean Stanton, who was in Alien.
- In the Super Mario Bros. movie, when Mario and Luigi are escaping from the police force, a news report identifies them as "alien plumbers".
Luigi: Aliens? We've gotta deal with aliens too?Luigi: We are? Cool!
- In Big Game, the first question Oskari asks Moore is what planet he's from, and the second is whether he comes in peace. While the escape pod does look like a space capsule, it has big USAF written on it, which should tip the kid off.
- In Spider Robinson's The Free Lunch, when the protagonists notice that there's something very odd about some of the attendees at the theme park where they live, their initial deduction is aliens. This being Spider Robinson, however, they're actually time travellers.
- Take Me to Your President by Leonard Wibberley was about a fellow nicknamed "A-1" from a small British town called Mars, who accidentally got loaded into an experimental rocket. When it landed somewhere other than it was expected to, and he came out wearing the space suit he'd found and saying he was from Mars, well....
- In Amy Thomson's The Color of Distance has the protagonist, Dr. Juna Saari, spend five years among the alien Tendu, who give her a moist color-changing skin and internal linings that keep her hair from growing and help with the planet's aversion to No Biochemical Barriers. When humanity comes back to pick her up, the first contact is with a suited man who thinks she's one of the Tendu, and she plays along for a bit before saying "I believe the line is 'Dr. Livingston, I presume?'"
- Christine Peacock sees mysterious lights in a field near the vicarage in Aunt Dimity Digs In, and she's convinced she saw aliens land there. She's even more convinced when a circle of trampled-down grass is found on the spot the next morning. In fact, Sally Pyne and one of the archaeology students were exercising there at night, mostly because Sally was embarrassed to be seen exercising.
- A long-running plot point of Animorphs. The Yeerks thought the kids were Andalites, and they are all too happy to let the Yeerks keep believing this, since it means their families will not be put in (more) danger because of it. The Yeerks finally figure it out near the end of the series, which marks the turning point as things quickly begin going to hell for everyone.
- Weirdly inverted in 1895 science fiction novel Journey to MarsFull Title by Gustavus W. Pope. When the protagonist sees Martians for the first time, he mistakes them for inhabitants of the land inside the earth's core (note that the existence of such a land was still considered possible by scientists at the time of writing, and the concept of extraterrestrials was still relatively obscure even in fiction).
- Depending on your definition of "another world", the fact Rincewind twice (Eric and The Last Continent) appears in a summoning circle and is therefore assumed to be a demon probably counts.
- In Death and Diplomacy, Bernice Summerfield, in an alien culture which has a wide range of races but no known contact with Earth, meets a guy who looks completely humanoid but, to an experienced traveller like her, his body language and so on is clearly off. This is her future husband Jason Kane, a genuine Earth human who was stranded in the alien culture following an Alien Abduction; he plays along for a while before making some sarcastic comments about being patronising to the natives.
- 21 Jump Street: In Old Haunts in the New Age, Doug is convinced he has encountered aliens, and that they moved his belly button. Turns out the lights he saw was just an advertisement by normal humans, not aliens.
- "Tomorrow is Yesterday" from Star Trek: The Original Series.
- Doctor Who: In the 50th anniversary special, when the Tenth Doctor is tracking down a shapeshifting Zygon through the woods, he comes across a large rabbit. He says he's not fooled and begins to give a Badass Boast, realizing midway through that it's a harmless Earth rabbit.
The Doctor: I'm the Oncoming Storm, the Bringer of Darkness, and you...are basically just a rabbit, aren't you?
- The I Dream of Jeannie episode "U-F-Oh Jeannie", where Tony was mistaken for a Martian by a group of rednecks in the Deep South.
- In the Jessie episode "Diary of Mad Newswoman", Jessie pretends to be an alien to teach Zuri a lesson about reading her Secret Diary. Unfortunately, Zuri finds out and does the same but with live special and effects. Cue to Jessie and Bertram being scared.
- In Kyle XY, Josh Trager claims, half-jokingly, that Kyle is an alien. (In fact he's an experimental clone with psychic powers.) Two years later, when Kyle finally reveals his history to the Tragers, he comments that Josh's guess may have been the closest to the truth.
- In the Lost in Space episode "Visit to a Hostile Planet", the Robinsons go back through time to 1947 and are mistaken for aliens when they land on Earth.
- In The Addams Family episode "The Addams Family and the Spaceman", the Addams are mistaken for aliens by the military, who approach them claiming to wish peace and asking them lots of questions. As a consequence, The Addams believe the army men are aliens as well because of the crazy coincidences.
- In the episode "Consequences," of CSI: NY, an urban paintball player is mistaken for an alien by a schizophrenic woman. She thinks the green paint dripping down his gear is his blood. He gets caught in the Bear Trap she had set in the alley to catch aliens and spends most of the episode in her bathtub.
- SG-1 deliberately invokes this when they're stranded in 1969, presumably figuring that it's a quicker explanation than the actual one. The main reason was to avoid paradox. (Although that didn't stop Jack from going by the names of fictional characters, some of whom already existed and others didn't, but who cares? They didn't want to endanger the Stargate program by accident.
- Subverted in Community: Abed plans to 'mess with' Troy by using the classic sitcom set up for this, except that he didn't fool Troy for a second.
- Done in the Torchwood episode "Countrycide", where the team thinks that some aliens are responsible for disappearances and attacks. Turns out, it's a bunch of humanitarians.
- In an episode of Newhart when some people see a U.F.O. the town is in the grip of alien paranoia. At one point a power outage hits the hotel and three figures wearing glow-in-the-dark gag antennae enter the lobby. After a moment's tense silence, one of them speaks:
- On I Love Lucy, Lucy accidentally gets a large racing trophy stuck to her head. Unable to see or get it off, she enlists Ethel to help her, necessitating a trip downtown to get some oil. They take the subway, Lucy wearing a veil in an unsuccessful attempt to look normal. At one stop, Lucy gets caught up in a crowd and ends up separated from Ethel and dragged off the train, losing her veil. Stumbling around blindly, Lucy asks a nearby man where she is. The man replies, "You're on Earth!" in a terrified voice before running for it.
- An Invoked Trope in The '90s remake of The Professionals. A former Cold War scientist is selling control of a laser-armed Kill Sat. To obfuscate his testing and demonstration of the weapon for an Arms Dealer he's selling it to, he has a couple of his men spread stories of UFO's. In the end everyone gets their just deserts, including the arms dealer who's arrested by CI5 for being an illegal alien.
- Played straight and then subverted in this strip from The Inexplicable Adventures of Bob!.
- Naomi of Dangerously Chloe who concluded Ted and co. as aliens due to a series of shenanigans, watching a cheesy B movie, and ruling out the existence of heaven and hell, Hilarity Ensues.
- Played with in El Goonish Shive with the perception of Uryuoms. Though they are aliens in the colloquial sense (as their species originates on another planet), they've been in hiding on this planet long enough that all the Uryuoms seen on-panel are not aliens in the legal sense, but natural-born U.S. citizens. Muggles don't seem to see past their Paper-Thin Disguise but magic users unaware of their legal status do identify them as aliens. Uryuoms can be rather insistent about correcting people about this.
- Aaahh!!! Real Monsters: In "Mayberry UFO", Ickis and his friends end up in the boondocks after taking a wrong turn in the sewers, and are mistaken for alien invaders by the locals. Unfortunately, in order to get home they have to find the only flush toilet around, which has been recently installed in the town hall.
- During the episode "Mush-Rumors" of The Adventures of Super Mario Bros. 3, a human family ends up driving into the Mushroom Kingdom by accident and are called aliens by one of the Toads, which then gets spread and exaggerated to the point where Bowser thinks they're an alien invasion force in disguise. The fact that they look not-unlike the human Mario and Luigi never comes up.
- The Simpsons: A crossover with The X-Files, "The Springfield Files" features Homer reporting an alien sighting. It turns out the whole time it was Mr. Burns, who was mistaken for an alien from the results of the various dubious medical treatments he undergoes and glowing green in the dark, a side effect of working at the nuclear power plant.
- Bloo mistakes Cheese for an alien in an episode of Foster's Home for Imaginary Friends.
- Spongebob Squarepants had an episode with them using Sandy's rocket to land "on the moon" (actually they circle around the moon and land back in Bikini Bottom) and go to hunt "moon clone aliens" which look exactly like their friends on earth.
- An episode of The Mask animated series featured a government agent and a scientist mistaking The Mask for a hostile alien due to a series of coincidences (not that it's hard to mistake him as such in the first place...)
Agent: Hmm...Subject has green skin. Imagine! Just like in the funny papers!
- Inverted and played straight in one episode of Viva Piñata. Fergie Fudgehog is conned onto going onto a defective rocket ship that crashes. When he comes out, his foggy helmet makes his friends look like aliens to him, and it makes him look like an alien to his friends! Needless to say, Hilarity Ensues.
- The Hey Arnold! Halloween episode. Also doubles as a Parody Episode due to all the Orson Welles references.
- In The Santa Claus Brothers, one of the elves is mistaken for an alien.
- In one episode of Class of 3000, Phily Phil is mistaken for an alien by an incompetent MIB-style agency when he crashes a spaceship he invented.
- In the South Park episode "Starvin' Marvin in Space", the people of Australia thought Marvin was an alien. To be fair, he did emerge from a spaceship.
- An episode of Gargoyles has an actual alien think the title characters are also aliens.
- Invader Zim:
- Aside from most humans falling for his Paper-Thin Disguise, "Abducted" inverts this by having a pair of stupid aliens abduct Zim because they honestly believe that he's a "normal human" like he constantly and loudly claims to be.
- In an unfinished episode, Zim tricks Dib into thinking Recurring Extra Poonchy, Drinker of Hate was an Irken invader. Hilarity Ensues.
- Phineas and Ferb, "Invasion of the Ferb Snatchers": A series of unlikely coincidences cause Candace to believe that Ferb is an alien. She's obviously wrong, but Phineas and Ferb are helping an alien rebuild his spaceship.
- Rocket Power features "It Came From Planet Merv", in which Twister automatically believes that Merv Simpleton is a strange creature from outer space right after Sam gives him a comic book just a day prior, and he even convinces Otto this illusion as the two believe the Stimpletons are going to zap the other two members of the foursome.
- Rocko's Modern Life has "The High-Five of Doom", where Rocko and Heffer think Filbert is an alien after reading his diary. It was All Just a Dream, but they were still freaked out.
- Rugrats did this several times:
- In "Aunt Miriam", Tommy and Chuckie become convinced that Tommy's Great-Aunt Miriam is an actual ant-monster from outer space.
- In "The Alien", Angelica couldn't fit into Chuckie's new playhouse and, out of spite, she tries to convince his friends that Chuckie is an alien and the playhouse is a spaceship in disguise.
- The Goof Troop episode "Close Encounters of the Weird Mime" had Goofy's attempts at taking up mime and Max and PJ's attempt at making a home sci-fi movie collide hilariously when the boys accidentally broadcast their video of aliens threatening the Earth.
- One episode of The Flintstones has Fred and Barney trying to help a pop-music group that has an "alien" gimmick get to the concert, at the same time that the radio announcer uses an overly-cryptic ad warning people "The Way-Outs are coming!" in a War of the Worlds-style fashion, and this makes the rest of Bedrock pull out the Torches and Pitchforks (he releases a retraction explaining that it was just a joke when the cops come barging into the studio and Just in Time to prevent said angry crowd from setting Fred and his friends on fire).
- In the Dexter's Laboratory episode "Smells Like Victory", an experiment gone wrong leaves Dexter's lab all smelly and dirty, which leads to a paranoid general mistaking it for a ground base for "evil filthy aliens". Meanwhile, Dexter is convinced by a garbled transmission that the safety-mask-wearing soldiers busting into his lab are the evil filthy aliens.
- Invoked in the Milly, Molly episode "Aunt Maude is an Alien". The two titular girls, in order to teach a rude boy Humphrey a "lesson", lie to him that the grumpy neighbourhood lady Aunt Maude is an alien.
- Gasp!: In "Alien Trash", Gasp leads a mission to the backyard to make peace with the aliens in the new spaceship...that turns out to be a worm farm.
- Get Ace: In the first episode, Ace's little sister Becky concludes that he's an alien impostor after witnessing him do weird things throughout the episode (which is him getting used to his new superpowered braces). Throughout the series, Becky tries to probe Ace or record his powers on video in order to prove that he's an alien, sometimes even believing that other people are aliens as well. She never considers any other possible explanation for Ace's strange powers, probably due to her pre-existing fixation with extraterrestrials. In one episode, Becky works with an alien hunter to help capture her brother, who turns out to be a real alien in the end (unbeknownst to her). So aliens do exist, but she's totally wrong about every person she believes to be one, and when a real extraterrestrial shows up, she's completely oblivious.
- The Shaggy & Scooby-Doo Get a Clue! episode "Lightning Strikes Twice" has Shaggy and Scooby get covered in lemon-lime pudding while attempting to enter Dr. Phibes' space station, resulting in Dr. Phibes' agents assuming that Shaggy and Scooby are aliens.
- The Daria episode "The Lawndale Files" is largely based on this. Some mysterious government agents coming to the school, plus various characters acting odd for various reasons, make Daria and Jane start to low-key wonder if aliens are invading, even though they both know that's ridiculous. Meanwhile, other characters misinterpret their comments to think that they're aliens.
Daria: No, I'm not saying Quinn's an evil space creature.
Jane: Oh, go ahead. It sounds so cool.
- Toward the end of The Little Rascals episode "Rascals' Revenge", Butch and Woim, believing themselves to have been sent to the moon, panic at the sight of Pete, whom Darla had disguised as a moon creature.
Butch: We're surrounded by aliens!
- King of the Hill: Done twice by the show's resident Conspiracy Theorist Dale Gribble.
- In the episode "Of Mice and Little Green Men", Dale finally figures out why his son is very different-looking from him and why his wife was able to conceive a child during his absence... aliens impregnated her! Believing his son Joseph is a half-alien hybrid, Dale gives him whatever he wants so that the aliens will spare his life in the oncoming invasion. Joseph, not being the sharpest tool in the shed either, also starts believing this and decides to run away to rejoin his "real" alien family. After that's resolved, Dale convinces himself that the aliens abducted him beforehand and used his DNA to artificially inseminate his wife.
- In another episode, Kahn's nephew (who only speaks Laotian) arrives in Arlen and meets Dale. From his eccentric clothing, high-tech car and saying "Arlen" as "Ay-len", Dale thinks he's an alien and agrees to get in what he believes is a spaceship and leave Earth. Then he sees that the car's clock is in military time, displaying 20:48, which he thinks actually is the year, causing Dale to think that he's a time traveler instead (which is somehow worse than him being an alien) and tries to escape the car, only to knock himself out while trying to do so.
- The Fairly OddParents special Wishology had Timmy Turner mistaken for being an alien by the agents of M.E.R.F. on the basis that there's no record of his existence (because Jorgen Von Strangle wiped everyone's memory of Timmy in a misguided attempt to protect Timmy from the Eliminators) and he is being followed around by an army of killer robots (the aforementioned Eliminators).
- After Yuri Gagarin became the first human to enter space and return successfully, a woman who saw his capsule land asked him, "Can it be that you have come from outer space?" He replied, "As a matter of fact, I have!"
- Most likely apocryphal, since it's now known that he actually bailed out of his capsule, and wouldn't have landed near it.
- Similarly, when John Glenn was orbiting in the Friendship 7 in 1962, the mission planners weren't exactly sure where the capsule would land - somewhere near Australia, as in any part of Australia or the surrounding oceans or islands for a pretty far distance. Glenn was worried what the aboriginal Australians might think when seeing a man in silver emerge from something that fell from the sky so he took a short speech with him rendered phonetically: "I am a stranger. I come in peace. Take me to your leader, and there will be a massive reward for you in eternity."
- Allegedly happened to an SAS troop doing a training exercise involving a High Altitude Low Opening parachute jump. Having landed in the middle of nowhere in the middle of the night, they walked up to the nearest farmhouse to get directions. A woman opened the door and found herself facing several tall beings dressed head-to-toe in black, with oxygen masks and blinking formation lights.
Troop leader: "Excuse me, ma'am. Can you tell us where we are?"
Woman: "Earth!" (slams door in their faces)
- One possible explanation for the case of the Hopkinsville Goblins is that they were simply great horned owls, combined with witnesses with too much alcohol in their blood.