With its dripping mouth and phallic head, the xenomorph is pure nightmare fuel, and every time it pops up in Ridley Scott's Alien, you know something terrible is about to happen. It stalks Dallas through the air ducts, makes short work of Brett and Parker, and does something truly awful to Lambert off-screen. But if you're looking for something that'll scar you for life, then it doesn't get any worse than the chestburster scene.
After stumbling into a pit full of leathery eggs, executive officer Kane (John Hurt) winds up with a facehugger attached to his head. And when the crew tries to remove the eight-legged monster, this nasty beast wraps its tail around Kane's throat, refusing to let go. Yeah, it's pretty sickening, but it only gets more disturbing from there. After the facehugger eventually falls off, Kane wakes up, and everything seems okay, until he starts suffering from the worst heartburn in history.
As Kane convulses on the table, his comrades gather around, trying to save his life … and that's when Kane's chest explodes, revealing a blood-soaked parasite. Naturally, the rest of the crew are completely freaked out, and some of the terror you see on-screen is real. The actors knew the chestburster was going to emerge, but they didn't know what it would look like, how it would happen, or how much gore was going to be involved. So when the worm from hell scampers off, you can tell the actors are experiencing some pretty serious nausea, just like the rest of us watching from home.