[[quoteright:350:http://static.tvtropes.org/pmwiki/pub/images/nightmare_2001_3184.jpg]]

This movie thoroughly endorses the trope NothingIsScarier and is pretty much [[UrExample the first movie]] to exploit the horrors of space (not counting '50s {{B Movie}}s), 11 years before ''Film/{{Alien}}''.
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* HAL is generally creepy all throughout the film, but the sequence where he [[spoiler:murders Frank Poole by ramming him with a space pod, severing his oxygen tube]] is outright ''terrifying'', not least because [[NothingIsScarier it occurs both offscreen and in complete silence.]] Not to mention the extremely quick series of jump cuts into the lens of HAL's camera before Dave sees Frank go flying past the screen.
** Even moreso, Frank's side of the experience. He's doing a routine repair job, when suddenly he is thrown out into space, his air hose torn. He can hear the flow of air get slower...and slower...as it gets colder in his suit...and harder to breathe...
** [[spoiler: For what it's worth, he gets better for 3001.]]
*** It may be worse in the film. We get [[SarcasmMode the sheer joy]] of watching his vital sign monitors fade to {{flatline}}s.
**** It gets worse. [[ToThePain Their nervous systems come back on right as they're dying.]]
**** That's actually a different scene, [[spoiler: where HAL kills off the astronauts in hibernation.]] Not that that's much better...
**** The scene in the movie isn't much better. After the aforementioned series of jump cuts, we see Frank tumbling through space, ''frantically trying to reattach his severed air hose.'' We quickly cut to Discovery where Dave is rushing out to the pod bay, and when we go back to Frank he's barely even moving...
** Related to this, some viewers noticed during HAL's game of chess with Poole, that HAL is cheating, announcing a wrong turn and even declaring victory when not in a position to do so. The computer they are trusting their lives on is able to lie! Possibly a foreshadowing that something's not right with HAL.
*** Alternately, HAL could be testing his ability to lie, as per his orders to not tell Bowman and Poole about the real intent of the mission. His primary function was to provide accurate information completely free from error, and as such had never lied before. He could not ignore his orders, but, given his subsequent actions towards the crew, nor could he stand lying. Distorting information, to HAL, must've been like trying to drown himself. He held his breath for as long as he could, and then desperately searched for a way out. He continued to lie out of necessity, figuring if he couldn't wholly stop it right then, at the very least he could end it sooner.
* [[BeamMeUpScotty "I'm sorry, Dave. I'm afraid I can't let you do that."]]
* ''Daisy, Daisy, give me your answer do...''
* ''I'm afraid. My mind is going. I can feel it. [[BrokenRecord I can feel it. I can feel it...]]''
** What really sells this is the way he says "I'm afraid". As he's saying it, you naturally assume (given the way he's been talking so far) that he's saying something condescending like "I'm afraid this won't work", or "I'm afraid you're overreacting, Dave", but instead he catches you off-guard by saying ''only'' those two words. A simple and piteous expression of fear. From a machine. The effect is nothing short of spine-chilling, on several levels.
* His nearly silent, ruthless murder of the three hibernating crewmembers also definitely counts. "'''LIFE FUNCTIONS TERMINATED'''" will haunt your dreams.
* The approach to the Monolith is one of the eeriest/creepiest scenes in film.
* The famous "Beyond the Infinite" sequence is more [[VisualEffectsOfAwesome awe-inspiring]] than scary, but when it's intercut with images of Dave [[GoMadFromTheRevelation FREAKING OUT]], it gets really creepy.
** It gets even creepier before that. There is a momentary sequence where Dave, wide-eyed in awe (to the point that his eyes are bulging out of his sockets) slowly starts to recoil from the intensity of the environment. The lighting and warping that continuously gets brighter and becomes increasingly distorted transforms Dave into this blue-ish, monstrous, yet somehow still human alien-thing. The sequence starts at around 0:40 and goes to 1:27 : http://www.youtube.com/watch?v=YbLRzabppus
** Actually, the scene goes on for quite a lot longer than that, lovingly extended in true Kubrick fashion to exactly the amount of time it takes for you, the viewer, to slowly go insane right alongside Bowman.
* Dave [[spoiler:''very'' slowly killing HAL by removing his memory]]. HAL's CreepyMonotone is enhanced when you realize that [[spoiler:''he'' is terrified and he can't even express it]].
** It's made a bit more unnerving when you realize that Dave isn't so much [[spoiler: killing HAL]] as he is [[spoiler: lobotomizing him]], and the fact that you can't quite tell if HAL is just trying to trick Dave by appealing to his more emotional side or if he's genuinely scared.
* The reason why Dave is going to the monolith. On one hand it's obviously because he wants to find out what is up with the thing, that [[spoiler: the government was willing to give HAL conflicting orders that led to the death of the rest of the crew.]] But on the other hand it's because he is essentialy stranded, since without [[spoiler: HAL or the rest of the crew]] he can't get the Discovery back to Earth, he is doomed either way.
** The novel adds a bit of FridgeHorror. Discovery only had enough fuel for a one way trip (somewhat justified as the original destination was Saturn), so once their mission was complete the crew was to go into hibernation and wait for the rescue ship ''that wasn't even built yet.'' It's very likely that if Bowman hadn't been able to reestablish contact with Earth after HAL went rouge, he very likely ''would'' have been left to die.
* [[spoiler: That damn Star Child at the end of the movie is pretty creepy, especially when he looks right at the audience.]]
* The bit with the monkey crushing the tapir skeleton with a club. This is the discovery of tools. If the music doesn't make it clear, it's supposed to be a singular leap forward for life on this planet. But then we realize it's just a more efficient way to break stuff and kill other monkeys. [[http://i.ytimg.com/vi/toNuups_j4A/maxresdefault.jpg The closeup on the ape's face]], complete with yellowed teeth and feral expression, is enough to send chills down your spine.
** On that note, the novelization (and the original screenplay) add some FridgeHorror to the famous MatchCut: the satellites that we see at the start of the Blue Danube sequence? They're launching platforms for ''nuclear weapons.''
* The monolith scene with the hellish [[DroneOfDread droning]] [[OminousLatinChanting choral]] [[http://www.youtube.com/watch?v=GgqI32JX_jY music]].
* [[http://www.youtube.com/watch?v=-iVYu5lyX5M Lux Aeterna]](2001:Space Odyssey). Funny nobody mentioned this one. It is even scarier in the movie, with Jupiter and black void on screen.
** [[http://www.youtube.com/watch?v=JPa4XAhSYhE Aventures for 3 voices and 7 instruments]]. The original piece may be NightmareRetardant, but Stanley Kubrick's "unauthorized remix" turns it into ''ultra super high octane nightmare fuel''. And it sounds like all he had to do was play it through a speaker inside a metal bucket.
** "Music/AlsoSprachZarathustra" itself; [[ScareChord that first trumpet blast]] can easily scar you for life if it catches you by surprise. Especially when walking through the halls at night when every dark doorway happens to looks like [[TheMonolith that goddamn monolith]].
** And then there's [[http://www.youtube.com/watch?v=hpJ6anurfuw this]]. Thanks a lot, Portsmouth Sinfonia.
* The scene where the leopard kills the monkey. It happens without any warning at all, and the thing's eyes glow so fiercely in the darknes that it practically looks demonic. The next scene, where we hear the leopard growling in the background as the apes cower in terror in their cave, sets the tone of the opening scene perfectly. We see how chilling it can really be to live on the bottom rung of the evolutionary ladder, always just one drought away from being wiped from existence for all eternity.
* For some, the man-apes in general are pretty damn unsettling. They're ''juuuuuust'' barely human enough that we can clearly see the roots of ourselves in them, but they're so hopelessly devoid of reason, restraint or empathy that they wind up invoking the UncannyValley in the most terrifying way possible. The two clashes between the rival ape tribes are especially chilling, even before they discover the wonders of weaponry and learn how to '''club their enemies to death with bones'''. That inhuman screeching and hooting will stay with you for weeks.
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