One of the most disturbing villains in recent memory is not a masked lunatic or a nefarious demon, but rather a seemingly innocuous Craigslist user. His name is Josef, and he can be found in Patrick Brice’s deeply unsettling found-footage movie Creep. Played by Mark Duplass, the character does not do anything overtly malicious for the majority of the picture’s runtime, but his unusual behavior and passive-aggressive comments become as terrifying as the actions of a chainsaw-wielding maniac. Through Josef, the film examines the horror of the subtle psychopath.

In Creep, Patrick Brice plays Aaron, a freelance videographer who responds to a Craigslist ad for a one-day assignment in a remote mountain town. That sounds like the setup for something sinister, and Aaron is skeptical from the get-go, especially when he shows up at the prearranged time to an empty house. Soon enough, though, Josef arrives, and he’s not some sort of obviously evil man running towards Aaron with an ax. Rather, he comes across as a normal dude getting back from a run, although there’s something off that we can’t quite identify. One of the first comments Josef makes to Aaron is, “You have a really nice, kind face.” Huh. That’s kind of bizarre to say to a stranger, right? Is Josef super friendly but a bit awkward, or should Aaron be worried? We expected his intentions to be pronounced straightaway, but so far that is not the case.

Our initial apprehension fades away after a few minutes with Josef, who explains that he’s a cancer survivor who was recently diagnosed with a brain tumor and has two months to live. His wife is pregnant, so he has hired this videographer to record a tape for his unborn son. In case he is not able to successfully combat the tumor, Josef wants his son to know what his father was like; he and Aaron will spend the day together capturing as much footage as possible. This situation is compared to the 1993 film My Life, in which Michael Keaton plays a terminally ill man making home movies to be given to his child. When Aaron decides he’s down for the job, Josef smiles and says, “I thought you were going to run away.” We feel bad for ever doubting Josef’s motives, and we want to give him a hug and tell him it’s all going to be okay.

Moments later, everything gets weird again. Josef says he’s going to get into the tub, and he invites Aaron to come in with him. Hang on…what? He wants a total stranger to film him taking a bath? Maybe he’s just an incredibly open person who doesn’t understand why that would make Aaron uncomfortable. Could that be it? Our opinion swings right back around as Josef says that he used to take baths with his dad as a child, and we breathe a sigh of relief. The initial invite into the bathroom was awkward, but when put into the context of a dying father who realizes he may never give his baby boy his first bath, it makes more sense.

This first act of Creep is a constant tug-of-war of emotions, as Patrick Brice revels in ambiguity and ensures we never know what to make of Josef. Is he literally about to break out an ax and chop Aaron’s head off? Or is he a lonely guy looking to make friends before death but who sometimes unintentionally drives them away? Both scenarios are equally plausible, so even during seemingly unimportant dialogue sequences, we never feel fully secure. Many found-footage movies waste the audience’s time with excruciating filler, but every millisecond of Creep speaks volumes.

As we soon learn, one facet of Josef’s peculiar personality is what he describes as his strange sense of humor. He’s always scaring Aaron just to amuse himself, such as when he sinks into the tub pretending to contemplate suicide before jumping up and screaming. Who does that? Later, he runs away from Aaron in the woods, only to sneak up behind him for a scare. This could be interpreted as the actions of a psychopath who is testing exactly how far he can push his victim before they snap and who is working himself up to finally strike. But it could also be that Josef merely has poor people skills and does not register that Aaron isn’t enjoying the humor. Because Josef appears to be so unassuming, Aaron can’t justify voicing major objections, and the cycle continues.

Josef also really overshares throughout the film, creating uncomfortable situation on top of uncomfortable situation. It starts with the bath scene, but there’s also the fact that he’s frequently making physical contact with Aaron when they don’t know each other. He often goes in for hugs, and during one dialogue scene, he begins rubbing Aaron’s arm, a gesture that’s really only appropriate in a close relationship. At lunch, when Josef apologizes for secretly taking pictures of Aaron, he says he wouldn’t have done it if he knew Aaron then the way he knows him now. He’s speaking as if they are suddenly friends of several decades rather than two people who met literally one hour ago. The hesitation in Aaron’s voice is easily perceptible, but he holds back and does not want to hurt Josef’s feelings.

For the majority of Creep, every unacceptable action Josef takes has an alternate explanation that makes us reluctant to judge. He scares Aaron in the bathroom, but then that’s because he was trying to lighten the mood. He takes pictures of Aaron without his knowledge, but then he profusely apologizes and says he did so because he was nervous about meeting a stranger. There is always just enough to rope Aaron back in and prevent him from running away.

It finally becomes clear that Aaron is in danger when he speaks with Angela over the phone, and the film reveals Josef’s entire story has been a lie. Angela, who is actually Josef’s sister and not his wife as previously stated, explains that her brother “has a lot of problems.” Even now, then, Aaron isn’t confident in what he’s dealing with. After Aaron escapes, Josef begins sending him packages in the mail, one of which contains a heart locket with pictures of the two of them. Josef is now quite definitively an unstable man who has gone full stalker, but does he have murderous intentions? To what extent is Aaron at risk?

The situation is horrifying regardless, and that is precisely because of the uncertainty. Villains are scarier the less we know about them, which is why it’s best to keep their backstory vague. Yet even with an enigmatic character like Michael Myers in the original Halloween, it’s still obvious that he’s the antagonist. We can point to the killer as being objectively evil and more like a monster than a man. Creep is so frightening because it suggests that identifying real-life monsters is rarely as easy as it is on screen. They don’t provide us unmistakable warning signs or bare the mischievous appearance of a Disney witch. In our world, outside the context of a three-act narrative and self-evident character roles, determining who might wish to do us harm is distressingly tricky.

In fact, most of us probably know someone like Josef in the first act of Creep. They’re outgoing and friendly, but they’re also a bit too open and they frequently invade the personal space of others without sensing resistance. They make jokes that leave their peers feeling extremely uncomfortable, justifying this as an example of their “weird sense of humor.” They’re always pushing people to see how much they will tolerate, instantly offering an apology when the behavior is questioned while never altering it in any way. Are we describing someone who is difficult but harmless, or someone who is dangerous and should be avoided at all costs?

We may not know the answer until it’s too late, as is the case with Aaron. Josef’s final move is to send Aaron a tape explaining that he has been pretending his whole life and has burnt every bridge, but all he really wants is a friend. In reality, this is merely yet another act of manipulation on Josef’s part, but Aaron isn’t convinced that this is the case. Despite dozens of red-flags, he wants to believe that Josef is kind at heart, and so he arrives at Lake Gregory willing to give him another chance. Ultimately, this trusting nature is his downfall.

No matter how cynical we might purport to be, most of us are very much like Aaron. We want to believe that others are fundamentally good in spite of their flaws. That person who has been treating me badly, we tell ourselves, is simply confused and imperfect, so they deserve a second chance…and then a third chance, and a fourth chance. We need to be cautious of the kind of over-the-top nutcase on display at the cinema, but not of seemingly average people. Right?

Unfortunately, real villains don’t wear crazy costumes or masks; they blend seamlessly into society, and their motives are just ambiguous enough for our guard to be lowered. That doesn’t mean we should live in a constant state of paranoia, but as Creep concludes, we ought to be as wary of emotionally abusive, toxic individuals as we would be of a Freddy Krueger or a Jason Voorhees. If only they were as easy to spot.