That banshee shriek you hear from the woods late at night or that barely visible figure standing in the dark background—instances where you might jump back and put yourself on high alert. Your palms get sweaty, your knees weaken and your heart starts racing. But why? Why do you feel so much terror?

The answer can be found in ambiguity, the unknown, the uncertain yet real possibility of danger—this is where the true horror lies.

Acclaimed horror fiction writer Stephen King proposes three different categories of horror: the Gross Out, the Horror and the Terror.

The Gross Out is exactly as it sounds: icky, disgusting monsters contorting every which way; think severed arms and body parts. Gore is the main driving force.

The Horror is what King defines as “the unnatural”: the thing that shouldn’t be possible and seems frighteningly out of place. Think of zombies or even the character Chucky, a sentient doll possessed by the mind of a serial killer.

The final category, the Terror, is what creators of horror strive to achieve. To best describe the Terror, imagine you are walking down the street at night: Everything is quiet, yet there is a thought in the back of your mind that you are being watched. You look around, only to find that no one is there—at least, that’s what it seems. You can’t point to a specific person or thing following your every footstep; you can only feel it.

At the highest level of horror, an atmosphere of ambiguity and uncertainty engulfs you. You don’t know where or what the danger is. You feel uneasy, creeped out—and because of this, you are truly frightened.

At the opposite end of the spectrum are the cheap tricks many horror directors employ to get a quick scare out of the audience. These are the jump scares and sudden loud noises which, though startling, do not evoke that uneasy kind of fear. These tricks rely on a fight-or-flight response—which various systems of the brain carry out, including the amygdala and hippocampus. The amygdala sends out signals to prepare the body to either defend itself (fight) or run away (flight). Stress hormones begin to flow and the sympathetic nervous system activates. We jump back because of the unexpected stimulus in front of us, hence “jump scare.”

But these tropes ruin the viewing experience. The best kind of horror avoids these pitfalls and instead creates tension by building suspense. There doesn’t need to be a scene where the monster is revealed in full form; subtle references or hints of its presence can work just as well, if not more so.

Two movies that utilize subtlety and ambiguity in genius ways are “The Babadook” and “The Killing of a Sacred Deer.”

“The Babadook,” which has become a cult classic since its release in 2014, tells the story of a single mother raising a troubled child. The film analyzes the effects of grief and loss and how it can alter a mother-son relationship.

The movie does a fantastic job of hiding the monster from the audience, whereas many horror films want to show it. There are only a few scenes where you can see the villain in complete form. The rest of the experience relies on tension and mystery—this is what King means by the Terror. You can’t see the monster, yet you know it’s there and can feel its presence. This is why “The Babadook” has been one of the only horror movies to terrify me and make me uncomfortable.

Working in tandem with “The Babadook” is “The Killing of a Sacred Deer.” The movie, based on the Greek myth of Iphigenia, follows the story of a surgeon who is forced to make an unthinkable sacrifice after earning the trust of a teenage boy.

Right off the bat, the dialogue is specific and overly formal to the point of being uncanny. Every character says exactly what they’re thinking or feeling, ironically leaving you with more questions than answers. During my first and only viewing of the movie, I frequently asked myself, “Why are they talking like that? Why does everything feel off?” Because it was off. That’s the whole point. The movie never fails to make the viewer uncomfortable, and in fact, the experience becomes more strange and unnerving the longer you watch. That’s the Terror working as intended.

These are only two out of an endless vault of horror films. Many others have their own unique strategies and scares. And this isn’t to say that movies with jump scares are automatically bad. They have their own place in horror tradition, but relying on that strategy too much is boring and ineffective. By depriving the viewer of knowledge and introducing uncertainty, they can have a  much more rewarding experience.

Scaring people is a delicate form of art. It is so much more than a quick spook here or a startling moment there. Horror is a whole experience that should tap directly into the deepest parts of your fear center. When you are terrified by what you don’t see, that’s how you know you are truly frightened.