Since time immemorial, storytellers have intertwined sex and scares to terrify audiences, and the combination works incredibly well. Long before the movie camera was invented, our ancestors told stories about incubi, succubi, and creepy fairies that abducted young women. And when filmmakers finally put these legends on the silver screen, audiences were introduced to a whole host of sexual nightmares.

Take Dracula for example. He’s a monster who sneaks into women’s bedrooms and assaults them in their sleep. The protagonist of Cat People refuses to consummate her marriage, believing sex will turn her into a wild cat, and the virgin always escapes the 1980s slasher while her frisky friends are all decapitated. In fact, director David Robert Mitchell based his recent hit, “It Follows”, on this very trope.

In other words, filmmakers use sex to make their audiences uncomfortable, and the guys who made Alien weren’t any different.

In the 2002 TV documentary The Alien Saga, Alien screenwriter Dan O’Bannon explained, “I’m going to attack the audience. I’m going to attack them sexually.” And O’Bannon wasn’t the only one who wanted to shock moviegoers. Both O’Bannon and director Ridley Scott were fans of a book called “Necronomicon”, a Lovecraftian grimoire by Swiss artist H.R. Giger. The book was full of disturbing sexual imagery, and Scott brought Giger onboard to give the Alien universe an incredibly eerie feel.

With O’Bannon writing the script and Giger designing both the set and the monster, it should come as no surprise that Alien is basically one big metaphor for sex, pregnancy, and rape. The entire movie is filled with phallic and vaginal imagery, from gaping doorways to penis-shaped ships. The Xenomorph itself has an incredibly phallic head, and its long, stiff second mouth—used to penetrate prey—is more-or-less the world’s most dangerous erection.

Perhaps the film’s most horrifying sexual image is the chestburster. The allegory begins when John Hurt wanders into a cave-like room full of eggs, possibly symbolizing a sperm entering the womb. When the leathery egg hatches, the terrifying “facehugger” latches onto Hurt’s face, forcing itself down his throat (strongly suggesting oral rape) and impregnating the man with an incredibly evil embryo. Moments later, Hurt “gives birth” to the creature, a larvae-like beast that’s the ultimate phallic symbol…complete with a slimy, wet mouth.

You get the point.

Rape is one of the worst crimes imaginable, and films featuring sexual violence often leave a permanent mark on our collective memories. That’s why men shiver whenever they hear the sound of banjos, why we can never look at pinball machines in quite the same way, and why Alien is still such a disturbing movie so many years after it first hit theaters.