[[caption-width-right:350:No one can hear you scream.]]

The ''Alien'' franchise has garnered a reputation for having some seriously nightmarish moments, mostly revolving around the animalistic and sexual horrors its alien antagonist unleashes on its unsuspecting victims.

* ''NightmareFuel/{{Aliens}}''
* ''NightmareFuel/{{Alien 3}}''
* ''NightmareFuel/AlienResurrection''
* ''NightmareFuel/{{Prometheus}}''
* ''NightmareFuel/AlienCovenant''
* The thought of extraterrestrial beings that [[FaceFullOfAlienWingWong invade your body]], through another being that technically ''rapes'' you, then burst out of your chest when you least expect it.
** Fun Fact: [[http://news.yahoo.com/zombie-fly-parasite-killing-honeybees-230200867.html there are real life creatures that reproduce like this]].
* For some reason the Aliens never managed to stick with a specific sound effect for their squeals and screeches throughout the movies, but the voices they've had over the years have always been unnerving and their screams in the second movie were arguably the scariest and most well known. For context, there's a shot during the hive attack where we see Hicks shooting something off-screen, and a Xenomorph lets out a [[UncannyValley human-like]] squeal. [[http://youtu.be/A7n3TFDF-mo?t=13s Listen here.]] Tellingly, their vocals in the second have been reused for most of their video game appearances and the second AVP movie.
** Then there's the haunting wailing screech that the Queen Xenomorph can give. One part cursing, one part lamenting, and all parts make-your-spine-shudder.
** The first movie had the Alien let out a scream that sounds very much like a monstrous baby when it scares Ripley near the end.
* In-universe, Ellen Ripley herself... before and after she was cloned. Feared by both Aliens and some humans. YEP, you heard that right. Even the ''XENOMORPHS'' are '''''afraid''''' of this one human.
* Here's a fun fact for your dreams: the Xenomorphs will NEVER be stopped. No matter how many you take down with power loaders or nuke from orbit (the only way to be sure), they're going to crop up on some other planet and start it all over again. You can thank both the Predators and the various humans greedy/stupid/mind-controlled enough to help the Xenomorphs spread and survive.

!!''Alien'' (first film)
[[caption-width-right:350:[[JumpScare Screeechhh!!!]]]]
* The original alien concept was made by the artist, H. R. Giger, who based his art style on his once frequent nightmares (ala the same one that caused Creator/HPLovecraft to introduce the concept of the EldritchAbomination). Despite the negative connotation of the word "nightmare", he apparently saw beauty in the creature.
** What arguably makes it worse is that, atleast to some viewers, the Xenomorph IS beautiful in an alien, otherwordly sort of way. It has a sleek, symmetrical design that doesnt trigger a horror response when just seen as an image.
** Just Bolaji Badejo moving around in the unedited test footage with a mocked-up Xenomorph head is very creepy. For that, we give him credit.
*** To expand: The guy's basically in his underwear, wandering around the set with a paper-mache alien head on his head, but ''still'' manages to create a sense of menace and alien surrealness that's quite unsettling.
* Giger's unique design of both the Xenomorph and the sets. ''You can see the human skull that the alien's head is [[http://www.prometheusforum.net/uploads/userpics/574/pLH1POJ57C3NQ.jpg based around]]''. Not to mention, the creature is so carefully designed to actually blend in with the rest of the environment. Meaning that these guys can and will appear everywhere. Made especially worse when you realize that the design of the Xeno often means you've been looking at it ''the whole damn time!''
** The first and probably the best example of this is when Ripley has just left the ''Nostromo'' and the Xeno to fry in the ship's explosion. So she relaxes and takes a load off, undressing, making sure the ship's working, until it reaches for her and reveals that it has been ''sitting right in front of her for the entire scene''.
** Something that makes the above scene even more terrifying is the fact that the Xeno DOESN'T attack. It makes its presence known just enough to get Ripley to back away, and then goes back to resting. And then we realize just how intelligent it is. It KNOWS that Ripley has nowhere left to run and it's perfectly happy to leave her alone until it gets bored.
* The famous John Hurt chestburster sequence, the gory details of which weren't told to most of the cast before the scene was shot (the look of horror on Veronica Cartwright's face as she's sprayed by a jet of sheep's blood is genuine).
** The absolute ''worst'' part, which is a lot more obvious in the director's cut, is that Kane doesn't immediately die once the Chestburster emerges. He's still moving and twitching even after it's run off.
** Apparently, Cartwright passed out during the scene after getting the blood in her face, and Yaphet Kotto (who played Parker) ran to his room afterward and refused to talk to anybody. It's made worse when you consider the cast didn't get ''too'' suspicious before filming the scene- after noticing ''everyone else on the set was wearing a raincoat''.
** Ron Cobb, one of the film's artists, sat down and saw the dailies for the chestburster scene. After sitting through the footage from all the cameras, he was so shaken up that he tried leaving the studio in a car that not only wasn't his, but it wasn't even the ''same color!'' Not to mention that he was blankly stammering and mumbling the entire time.
** Something to keep in mind is the historical context of the film and its impact on the genre. Until ''Alien'', most extraterrestrial films were low-budget scifi or less serious in nature. This film combined horror with special effects in a way that was completely new to EVERYONE, whether cast member or audience viewer. It's not hard to understand why everyone was so shaken up by it. It was literally unlike anything seen before.
** The cast ''did'' know what was going to happen, they had read the script (which describes the scene in fairly graphic detail on it's own). What they ''didn't'' know was what the practical effect would look like, since no one had attempted something like this before. Even the effects team weren't certain if they'd be able to pull it off. They'd pepped the rig, complete with a scored t-shirt that the alien prop should be able rip through, and on their first try, it didn't. [[ThrowItIn This made it into the film,]] the first shot where the chestburster pops and pushes out the shirt, and everyone freezes. The actors in a fairly genuine "what the hell was ''that''?, the crew in an "OhCrap, it didn't work!" After a beat, everyone remembers their jobs, the crew makes the gag work, and the result is one of the most terrifyingly iconic scenes in cinema history.
* The incredibly eerie exploration of the derelict spacecraft, including a strange alien skeleton in a chair, with no explanation of what the ship is or to whom it belonged given.
* There is a long, slow scene of Brett looking for Jonesy, finding him in a room with water dripping from the ceiling and chains hanging from the vents. This is before the adult alien has been seen at all and audiences are expecting it to still be tiny. In one brief shot of the ceiling, the alien is fully seen hanging from the chain above Brett, but from it blending in with the scenery the audience does not even notice it. They only realize they were looking right at it on a second watch, [[spoiler:after it has lowered down to snatch Brett]].
** Brett's death is terrifying, as in the theatrical version, Brett stares at the Alien for a second before the Xeno kills him with its inner mouth. In the extended edition, the Alien pulls Brett towards him while using its tail to ensure he cant run, and lets Brett scream what is it and calling for help before he is killed. The Alien had the chance to kill Brett quickly, but instead let him stand there terrified. The Alien enjoyed watching Brett look terrified, indicating it can actually be sadistic and genuinely evil.
* The scene with Dallas in the air vents, featuring one of the biggest JumpScare moments in film history. Dallas appears to have climbed down a ladder to safety from the approaching alien, only [[spoiler:to turn around and find the alien ''right in front of him'', screeching and reaching out for him before the camera shorts out]].
* The absolutely nightmarish scene of [[spoiler:Parker and Lambert's deaths, seeing Parker killed by the alien's "second mouth", and not even [[NothingIsScarier seeing]] what it did to Lambert (apart from moving its bladed tail [[DoesThisRemindYouOfAnything up between her legs]]), only hearing her anguished death cries over the radio]].
** The book "Alien: Out of the Shadows" revealed what happened to Lambert: [[spoiler: the Alien ripped a hole in her face]].
** However, one detail adds a more disturbing subtext to [[spoiler:Lambert's death]]. [[spoiler: She]] is wearing thick-looking pants and boots when the alien's [[spoiler:tail is seen moving between her legs]], but when Ripley finds [[spoiler: her]] body, [[spoiler: she]] is barefoot and appears to be no longer wearing pants. FridgeHorror kicks in when you remember the filmmakers stated the Alien is designed to be the embodiment of the fear of rape.
* The climax of the movie, following Ripley as she beelines for the escape pod, is one of the most intense chase scenes in film history [[spoiler: even though the alien isn't actually chasing her, and is eventually revealed to have turned around and gone in the complete other direction.]]
** During the entire movie, Ripley manages to take nearly everything pretty well, including [[spoiler:finding Parker and Lambert's mutilated corpses and finding Dallas and Brett half-transformed into eggs]], so seeing her lose her cool and almost break down while running through the Nostromo's claustrophobic hallways inspires a deep feeling of terror in one's heart.
* The sight of the Alien/Xenomorph being jettisoned into the black, lonely void of deep space after getting blasted by the ship's engines.
* In the director's cut of Alien, there is also the scene where Ripley finds [[spoiler:Dallas and Brett in the process of being changed into alien eggs]]. It is not only revolting, but it's also UncannyValley.
** It also adds to, yet again, depending wether or not deleted scenes are canon (It IS a deleted scene, after all. Plus, the Xenomorphs are never seen doing that again in anything else, so wether or not the scene is canon is quite debatable.) another amount of FridgeHorror. This means that if this scene is canon, then this means that the Xenomorphs don't NEED a queen in order to make eggs. They can literally MAKE MORE from the bodies of those who have been face hugged if they lack one.
* The whole scene where [[spoiler: Ash is revealed to be a synthetic]], up to his death, is this.
* [[http://www.youtube.com/watch?v=DGAHtWV7Ua8 The original trailer]] for the film is 120 seconds of condensed and highly efficient Nightmare Fuel. No bombastic score, no booming voiceovers, no stars' names blasting onto the screen; just quick flashes of the most disturbing scenes in the movie punctuated with a rapid HeartbeatSoundtrack and the intermittent sound of a frighteningly inhuman wail before the iconic tagline appears:
--> '''In space, no one can hear you scream.'''
* In 1984, Argus Press Software released an Alien game for the C64, Amstrad, and ZX Spectrum. The crew of the ''Nostromo'', following the gory birth of the Alien, must track it down and either kill it or space it (or activate the self-destruct sequence and abandon ship). Naturally, trailing the Alien puts you at risk of an encounter that you are unlikely to survive. Oh, and the poor sod who gets a facehugger clamped to their face isn't always Kane, [[spoiler: nor is the traitorous android always Ash]].
* As noted above, there are several times throughout the film where the Xenomorph is so well camouflaged that it can be placed right in the plain sight in the frame and still not be seen until a second viewing [[spoiler:like with Brett and Dallas's "death" scenes and the last jump scare in the escape pod]]. Even on a first watch, the audience eventually catches on to this, and it makes the dark, flashing corridors of the Nostromo even more terrifying: every single pipe, tube, or wall could be the Xenomorph.
* When Kane wakes up after the facehugger releases him, someone asks him what he remembers, and he says "Just some horrible dream about... smothering." ''He doesn't remember the facehugger grabbing him.'' A perfectly logical defense mechanism for the alien, preventing someone who's been grabbed from alerting others to their condition and threatening the embryo, but it also means [[ParanoiaFuel a person could be gestating an alien and have no idea until the pain starts.]]

!! Expanded Universe
* ''NightmareFuel/AlienIsolation''
* ''NightmareFuel/AliensColonialMarines''
* ''NightmareFuel/AlienVsPredator''
* In the comic/novel ''Aliens: Labyrinth'', a critical piece of backstory involves the story's MadScientist. When he was younger, he and his fellow colony members were captured by a colony of xenomorphs that was dying due to some sort of disease. Trapped in the hive, he only managed to survive by [[LesCollaborateurs deliberately working with the aliens to nourish and care for the other captives]]. Among the horrors he sees is a former female friend of his who has had facehuggers ''implant her womb'', causing her to swell up in an obscene parody of pregnancy before she is torn apart by three grotesque half-developed adult xenomorphs, still linked to her by umbilical cables. Eventually, he finds the source of the disease and uses it to poison the colony, but the colony tries to use him to breed with a female captive to create new hosts. He's presented with a woman who has had her limbs ''gnawed off'' and cauterized, driven quite insensible by her abuse at the hands of the xenomorphs. [[spoiler: The woman is his mother.]] Driven mad by the realization, he gives her a MercyKill. For this, the queen has him implanted with the last surviving facehugger. When he wakes, he finds the plague has finished destroying the colony and the chestburster inside of him is stillborn. Then he has to escape from the hive and perform surgery ''on himself, without anesthetic'' to remove the embryo before it decays inside of him and gives him fatal blood poisoning. It's no wonder he's gone absolutely insane!
* The early ''Aliens'' comics provide a truly horrific explanation for why humans constantly grab the IdiotBall when it comes to looking for the Aliens and bringing them back to Earth. It's ''all part of the plan'', orchestrated by the Queen Mother on the homeworld to propagate her species by using a whole planet. It's hard to decide which is the scarier part:
** That the Queen Mother becomes the subject of her own maternal feelings, to the point of ''begging for a Facehugger''.
** That the humans, in essence, are the Sci-fi equivalent to ''{{Sex Slave}}s''.
** That the psychic signal is spread by a madman who sees the Aliens as gods.
** That this is all simply part of the Aliens' life cycle and has no malice at the core.
** That it's clear that this entire process has been played out on other planets before and will continue to play out until every Alien is dead... which is going to be very hard considering that the Franchise/{{Predator}}s have spread them throughout the galaxy, if not the universe, as yet another prey species of theirs.
* In one of the novels, a group of marines goes to the Xenomorph homeworld to serve as facehugger bait. One of them points out 2 facts.
** The Xenomorph is an invasive species most planets cannot handle, whereas on its homeworld, it probably struck an ecological balance with other species.
** On its homeworld, it may not be the dominant lifeform.
** One character thinks about the hypothesis that the Alien's have acid blood because ''it makes them taste bad.'' '''What the hell could be out there trying to eat the fucking ALIEN?!?'''