It Follows

It doesn't really. A collection of scattered, potentially interesting ideas fizzle out in this silly horror movie. The premise is that something scary is unleashed against you when you have sex. In real life this may range from HPV to gonorrhea to herpes to AIDS, all way scarier than the people (zombies? undead? It's not clear) who appear to be following the poor horny fools who shag. Imagine if you took these sexually invoked zombies to instill sexual panic in the general population. A disaster movie about abstinence! That would be interesting. But It Follows sticks to a bunch of inarticulate, generic young adults and wastes every opportunity that its own premise promises.
I was wondering if the easy way out from this horror would be to simply use a condom, but the movie never addresses the possibility, as it doesn't really care about the rules it sets up and then changes at will. Character and motivation are never established, so we don't understand why the heroine of the movie makes crazy choices, for instance, as when in the throes of sheer terror she decides to run to a park alone at night and sit on a swing. Unless there are good reasons for the bewildering choices characters make in horror movies, the audience is distracted by the whys. As in, why are you so stupid?
Writer/director David Robert Mitchell toys with the disturbing notion that this post-sexual haunting may be a cruel prank, a sort of urban legend that drives people crazy, since no one else can see the followers. What if it is all in their heads, a sort of suggested hysteria? That's the movie I would have loved to see. Psychological terror is always far scarier and suggestive than the supernatural. The director flashes this idea at the audience but soon abandons it, as he does every potentially interesting story turn. He skims over the juiciest parts of his own premise.
It Follows has all the elements of a classic horror movie (and too many of its well-worn tropes) yet Mitchell doesn't have the attention span and the focus to carry them out. For instance, he establishes that the girl has two creepy teenage neighbors who like to spy on her. But he underestimates their potential to confuse and soon forgets them. The movie is full of such arbitrary and absurd nonsequiturs.
Still, it is fun to find yourself scanning the frame for these shapeshifters, who sometimes look like normal people, sometimes are naked, sometimes look like ghouls. It would be nice to know who they are: the bereft after sex? The people who don't have any? It's a mystery.
It is fun to not know who is real and who isn't, and Mitchell handles this particularly well in one scene. But then random stuff starts happening and one loses faith in a movie that does not follow its own rules. There is one effectively staged, truly scary moment, achieved with nothing but the smart use of a tall guy and excellent timing.  The rest is a lot of aimless padding and lazy writing.
The overwrought, manipulative music score doesn't help. There are a couple of well-staged moments (ripoffs of Polanski and David Fincher) within disorganized sequences, but the movie makes no sense. The ending is a total dud. I didn't follow it.