What is the scariest science fiction or fantasy film of all time? Which movies stand above the rest off all horror flicks as the most terrifying?

The staff at io9 has painstakingly selected the best of the best, and compiled our ultimate list of the scariest movies of all time. Over the next few days we'll be releasing our picks, ten at a time. Today, check out numbers 41 through 50...

50. Something Wicked This Way Comes (1983)
What: Loosely based on the 1962 novel by Ray Bradbury, this poor film was caught between a rock and a hard place as Disney gobbled up the rights hoping to widen the studio's "family feature" reputation. But even though director, Jack Clayton, tried his best to dilute the Bradbury horror plenty of unsettling oddities and creepy scenes landed on screen. The movie follows local boys Will and Jim as they get tangled up in the devious going ons at Mr. Dark's (Jonathan Pryce) traveling carnival. At this nightmare festival, Mr. Dark grants the townsfolk's wishes, but of course every wish comes with a horrible price.
Why: This movie scared the apple juice out of half of the io9 team. The pace, the people, the weird animated effects looped in with real life action still haunts our darkest fever dreams.
Scariest Scene: There's plenty to choose from, including a little boy's bedroom covered in real life tarantulas. But perhaps the scariest scene is also the most infamous. Mr. Dark's on the hunt for the main characters, and he approaches Jason Robards asking if he's seen either boy. Opening up his hands, Mr. Dark reveals two portraits penned on the inside of his palms. After being lied to, Mr. Dark furiously squeezes his hands smearing the ink and causing the boys (in real life) to bleed.

49. An American Werewolf In London (1981)
What: Two American youths run into a werewolf while backpacking through the English countryside. One dies, the other is cursed with the mark of the wolf.
Why: John Landis' direction changed the way we viewed the Classic Universal Monsters. He turned the whole canon on its head, playing with the rules and delivering one of the most legendary werewolf transformation scenes ever put to film, with the help Rick Baker of course. Being a werewolf was grotesque, dangerous and most of all painful, as the audience soon found out — through a set of screams and bone-breaking snaps. It's terrifying, disgusting work.
Scariest Scene: Even though we bow our heads to the renowned werewolf transformation, Jack's entrance was what really made our jaws drop. Doomed to walk the Earth in purgatory Jack's rotting corpse goes from gruesome to putrid over the course of the film. You want to laugh, but you're too busy just starring at the amazing gore work.

48. Midnight Meat Train (2008)
What: Bradley Cooper thinks he's caught the serial killer of the century on camera. But what he discovers is infinitely worse, and severely bloody. Based off a short story from Clive Barker this slasher flick is so much more than just a murderous butcher, Mahogany (Vinnie Jones), gone mad.
Why: We gotta give Meat Train props for all the insanity it hosed all over the audience. And the action, oh the action! There's a decapitated head POV shot in this film — and that's after the slasher smacks one victim so hard in the head, his eye pops out at the camera. It's delightfully gory and gruesome.
Scariest Scene: The finale. Which we've included above and is VERY VERY SPOILERIFIC, WE WARN YOU. Who knew Midnight Meat Train wasn't just your everyday cut-em-up flick? What's lurking beneath the surface of this movie was absolutely terrifying, and it kind of blindsided the audience in an exceptionally aggressive manner. Kudos for getting us off guard (and for ripping out Bradley Cooper's tongue and eating it for a snack, subway conductor).

47. Re-Animator (1985)
What: Shocking, funny, gory, and starring a very young, hot Jeffrey Combs, this movie from brainy schlockmeister Stuart Gordon is the very loose retelling of an H.P. Lovecraft short story called "Herbert West, Re-Animator." Basically it's the tale of a mad scientist, West (Combs), whose rivalry with his medical school professor leads to a terrifying discovery: a glowing green serum that can reanimate the dead. Unfortunately they come back as mindless zombies — but West's rival, after an unfortunate beheading accident, is reanimated into the sole creature who can rule the zombies with mind control. Fighting ensues.
Why: Creative effects and delightfully over-the-top performances elevate this flick from B-movie barfatorium to genuinely horrifying weirdness.
Scariest Scene: One of the first things that West's rival does, after discovering that he can control the zombies with his mind, is order his minions to fetch the young lady he fancies. Then he straps her to a table and . . . well, uses his head. Watch this NSFW clip if you dare. Luckily, West stops him before things get really horrific.

46. Cat People (1942)
What: Panther people who kill! Directed by Jacques Tourneur, this movie revolves around the very chic Irena, who uncovers a family secret — she's a cat person. But there's a way to avoid all the cat killing: never get sexually aroused. This becomes difficult when she falls in love and gets married. Putting off their honeymoon night, Irena discovers that her husband's assistant has been making moves on her man. Then the cat-stalking begins.
Why: It did so much with so little. Also it's a black and white movie with zero gore, and that makes Cat People scarier.
Scariest Scene: Irena follows the assistant all over town and eventually corners her in a pool. Terrified the poor girl jumps in the middle of the water (as cats are really pool pets) the lights go dark and all you hear are terrifying cat growls and the screams of the assistant. It's fantastic dread and tension, and an absolute staple in horror shadow work. Plus, it's scary!

45. La Conquête du Pôle ("The Conquest of the Pole") (1912)
What: One extremely hungry ice giant.
Why: Because he's still pretty disturbing a century later.
The Best Scene: This 30-minute silent film by pioneering French filmmaker Georges Méliès was an adaptation of Jules Verne's 1866 novel The Adventures of Captain Hatteras. It's a pretty whimsical film with one sinister exception — a fantastically creepy sequence when the ice giant bursts out of the ground and begins consuming the Arctic explorers. Méliès depicted the creature using a massive puppet, which is impressive today and almost certainly made audiences' heads explode 100 years ago. The giant shows up at 5:15 in the above clip, and you can watch the film in full here.

44. The Birds (1963)
What: Alfred Hitchcock unleashes the fury of the winged beasts on a small town, for no other reason than the birds just want us all dead!
Why: No one thought birds were scary, until this movie. Not even the sexy Suzanne Pleshette was a match for these beaked beasts — the birds killed her in front of a small child! Plus this movie works wonders, without doing a thing. For minutes nothing actually happens while a flock of crows menacingly sits on a school playground, the scariest part is just getting around a giant murderous collection of blood thirsty peckers without setting them off.
Scariest Scene: Lydia (Jessica Tandy) finds a dead man with his eyes pecked out. BIRDED.

43. The Blob (1958)
What: Classic 50s alien invasion flick about a red goo from space that consumes everything it touches, made for a tiny budget by a director who had never done anything but church movies and instructional films. Essentially, it was the Paranormal Activity of its day, a cheap flick starring a cast of unknowns (including Steve McQueen in his first role), which became a smash hit. Even the theme song topped the charts and sent Americans into blob-mania.
Why: An original monster idea, simple but devastating, crawls its way through a believably confused small town. Oddly realistic, and therefore more terrifying than other giant monster movies of the same era.
Scariest Scene: There are a lot of scary scenes, including the first sighting of the Blob eating an old farmer's arm. But the classic crazy-mad-terrifying scene is when the creature - grown giant after eating a ton of people - oozes its way into a movie theater and menaces the audience, who stampede into the street. It's scary, plus the movie theater is showing a horror movie, which gives the whole thing a nice touch of meta humor.

42. The Crazies (2010)
What: A remake of the little known George Romero movie with the same name, The Crazies takes place in a small town that is exposed to a secret government virus which turns the citizens into, well, crazies. Their only motive, kill everything and everyone around them.
Why: Director Breck Eisner proved that you didn't need big stars or a big budget to produce big chills. This movie was slick as hell, once the Trixie virus was established the hits just kept on coming. But the best part of it all was the character motivation, get out. That's it, they just wanted out of town and together they devised non-insulting and fairly intelligent ways of getting the hell out of there. They kept is simple, what's this farmer doing, oh locking his family in the closet and then burning down their house.
Scariest Scene: The Morgue.

41. The Mist (2007)
What: Frank Darabont's most controversial work, adapted from a Stephen King novella. A large group of townsfolk seek refuge in grocery store while the Earth is covered in a strange mist. Inside the mist, monsters, bugs and certain death. As the days go by, the group splits and religious nut job Marcia Gay Harden convinces her followers that they've opened the gates of hell, and the only way to close those gates is with the blood of the innocent.
Why: The best kind of monster movies are when the real beasts are ourselves!
Scariest Scene: Andre Braugher takes a walk in the Mist.

Additional writing by Cyriaque Lamar and Annalee Newitz. Top image by Joel Johnson.