Because what’s scarier than having your body taken over against your will by an alien being? Or, as it’s more commonly known: pregnancy.

Of course, in most cases, when a woman is pregnant it’s not because her husband has arranged for some neighborly witches to have her raped by Satan in exchange for a boost to his acting career. The premise is ludicrous, but Rosemary’s Baby unfolds slowly and, by focusing on the mundane details of Rosemary’s life as well as the subtle horror, quite believably.

Lovely yuppie couple Rosemary and Guy Woodehouse, played by Mia Farrow and John Cassavetes, move into an old New York City apartment building (played by the Dakota) with a disconcerting history of violence and witchcraft, which they of course ignore. Their next door neighbors, who they can occasionally hear through the walls in certain rooms, are the pushy and snooping though seemingly well-meaning Castavets (Sidney Blackmer and the fabulously irritating Ruth Gordon, who won an Oscar)– though to be fair, their pushiness only makes itself felt after their young female house guest kills herself, and they realize Rosemary is… fertile.

Mia Farrow gives a great performance, from glowing, beautiful, pliant young wife to a ghostly, half-mad, desperate soon-to-be mother. The character’s passivity can be frustrating – she lets herself be pushed into doing all kinds of things she doesn’t want to do by her husband, her neighbors, and the doctor they corral her into seeing – but it’s also understandable; Rosemary doesn’t want to make a fuss, doesn’t want to be rude, doesn’t want people to be upset with her, isn’t even sure she’s right. It’s in those scenes that Rosemary’s Baby becomes something of a feminist parable, not something I expected from Roman Polanski (maybe the ultimate “love the art, hate the artist” example, for me). The real horror of Rosemary’s situation comes not from being raped by the devil and impregnated with his spawn but from feeling cut off and powerless, used as a vessel for childbirth and not much else, ignored, told not to read or do or think anything for herself. By the time she gets up enough panicked courage to take action, for the sake of her unborn baby if not herself, it’s too late.

That’s another credit to the movie: it takes Rosemary nearly the entire running time to figure out what’s happening, whereas the audience is clued in from the start – to the fact that something sinister’s afoot, at least, if not precisely what. And the somewhat surprising ending is widely known, at this point (“What have you done to his eyes?!“). But while it’s frustrating to watch Rosemary become entangled in this sinister conspiracy over the course of hours, Polanski uses that frustration to invest the audience further, to deepen the viewer’s discomfort and tension. There are few movie characters I’d like to eviscerate more than the Castavets and their friends, especially that Laura-Louise. As Roger Ebert wrote in his review,

When the conclusion comes, it works not because it is a surprise but because it is horrifyingly inevitable. Rosemary makes her dreadful discovery, and we are wrenched because we knew what was going to happen –and couldn’t help her.

For all its horror, Rosemary’s baby is often wryly funny, and the movie keeps its sense of humor til the very end (when Rosemary drops her kitchen knife in horror near her baby’s bassinet, Mrs. Castevet picks it up and quickly rubs at the mark it left in her nice wood floors). Still, that end comprises the complete triumph of evil – the banality of evil, in fact.

Use protection, kids. Beware of too-good-to-be-true New York City real estate deals. And never, ever marry an actor.