John Carpenter's body horror classic still freaks people out with its gruesome defibrillator scene. Besides the amount of fake blood and multiple moldings of the actors, they also used double amputees to simulate the ripping out of the arms.
The mythological creatures Ray Harryhausen brought to life in this adventure movies came from his "Dynamation" technique. It was a split-screen process that put the stop-motion animation in the middle of live action shots.
The space drama has amazing scenes where the actors floated in what appeared to be zero gravity. Instead of holding them up on wires, the film used the planes NASA uses to get the astronauts used to weightlessness and built sets inside of one. They only had 25-second intervals of recording but they recorded over four hours of weightlessness.
The overhead shots used lots of small scale models, but the famous face-melting scene used some unconventional equipment. Alginate, which is used to make the impression of your teeth, was used as the material on top of the stone skull that was melted by a heater. The effects team though it was too gory, so they added the pillar of fire to tone down the shot.
One of the reasons you famously don't see the shark until late in the movie is because they animatronic shark Steven Spielberg used kept breaking down. Another important thing to know about "Bruce" (as the shark was called) is that it doesn't look anything like an actual great white. That actually makes it look scarier.
Years before the xenomorph was CGI, the original was a 7-foot 2-inch man from Nigeria in a bodysuit. For the chest-bursting scene, it was the difficult choice of a cavity filled with whatever the special effects team picked up from the butcher's shop. Apparently, seafood is the best option for the nastiest look.
Director Stanley Kubrick hired NASA consultants to make the movie as scientifically accurate as possible. He even had a massive Ferris wheel created to simulate the artificial gravity on the spacecraft Discovery.
The room was refrigerated so the audience would see the breath of the characters in the exorcism scenes. And the head-spinning scene was just a life-sized model of actress Linda Blair. In behind-the-scenes footage, you can see the model does not hold up well in well-lit areas.
The lighted green tips were worth thousands of dollars (of 1950s money) and composed of copper wires and circuitry so the model could light up. The alien ships moved on overhead tracks and multiple exposures were used to make the heat ray effect.