The Upside Down isn’t something you see as much as hear. Otherworldly howls wash over waves of striding synths in the alternate universe at the dark heart of Stranger Things, warning us not to trespass, even before the first flakes of ash start to fall. There’s no question that the sounds themselves are unsettling — but understanding why they strike fear, requires a little more self-reflection. What we find most frightening about the sounds, says David Toop, Ph.D., a professor of audio culture at London’s University of the Arts, is the fact that we can’t pin them down.

Having watched a few episodes, Toop, author of Sinister Resonance, an exploration of the literary, cultural, and evolutionary history of frightening sounds, explained to Inverse that the use of electronic instruments, bodily sounds, and disembodied noises on the show’s soundtrack all exploit one of the human mind’s most traitorous psychological flaws: a deep-seated mistrust of our own hearing.

“All of these different characteristics make sound slippery — and to many people untrustworthy,” he tells Inverse. “These elements combine together to make a very powerful medium as a trigger for our emotions.”

In the world we live in, the sense of sight trumps all: When we hear a rustling in the woods, we’re not reassured until we catch a glimpse of a moving animal. If a door creaks in the night, we sit up with a jolt to check who’s there. The Stranger Things score banks on the basic assumption that we fear what we can’t see, crafting a sinister collage of noises with no clear origin. On the track entitled “The Upside Down” on Stranger Things, Vol. 1, the yowl of a wolf — or is it a siren? — suddenly emerges from the swirling synth soundscape about halfway through the song, sending shivers across the listener’s skin. What is that, we ask, and where the hell did it come from?

“Sound has the property of coming through walls, through windows, traveling long distances, so this disembodiment is very much a part of the character of sounds, and that can make it very eerie,” Toop says, noting that in horror novels and films, it’s often the things we hear, not the things we see, that signal to us that something is wrong. Unlike the visual world, the auditory world isn’t tangible, comprising instead, of vibrations and air-bound waveforms. Recorded sound is always in motion, even in playback; in other words, it’s constantly slipping from our cognitive grasp. You can’t trust what’s elusive.

Adding another layer of disembodiment to the score is its exclusively electronic instrumentation. By strictly using a palette of synthesizers, SURVIVE, the Austin-based electronica band behind the show’s soundtrack, weaves our historical unease about electronic instruments into an already-unsettling soundscape, explains Toop. While synth-based music, adopted by ear-friendly artists like Justin Bieber and The Weeknd, may seem commonplace, it was once considered too unearthly-sounding to be comfortable, he says. As it emerged in the 1960s with avant-garde pieces like Karlheinz Stockhausen’s “Telemusik,” synth was entering public consciousness at the same time as the first moon landing — the U.S.-Russia Space Race — and sci-fi films, like 2011: A Space Odyssey, cementing an uneasy association with the vast unknown that, Toop argues, still persists today.

Part of what makes electronic sounds so haunting, is the fact that they’re unnatural. As with the forest’s rustling trees or the groaning floorboard, we don’t really know where the sounds of a laser blip or a swirling phaser actually come from. We accepted that machines were capable of making sounds we’d never heard before, but our lingering perturbation bred the idea that sound could be made without human intervention. The use of automated arpeggiators in the menacing Stranger Things intro, Toop points out, requires so little programming that it is at once “incredibly impressive” and “quite disturbing.” Without a physical, visual body to peg the origin of a sound to, our imaginations are free to run wild. “It makes you think: maybe these instruments could take over,” he says.

What might be most unsettling, however, is when our search for the origin of a frightening sound leads us to our own bodies, he says. In Stranger Things, when lab technicians, clad in full-body hazmat suits, make their first foray into the Upside Down, it slowly dawns on us that the thick, muffled sounds we’re hearing are in fact the amplified, labored wheezing from the mouth-breathers beneath the helmets. They’re similar to the chilling, strained exhalations you hear in “Cops Are Good At Finding,” on the show’s soundtrack. “There’s something very sinister about that,” Toop says. “I think what that’s about, in the end, is our fear of our own bodies.”

Stranger Things, Vol. 1 debuted at number 24 on Billboard’s top 200 chart, selling 14,000 copies in its first week, and thereby thwarting the idea that discomfort is in any way a deterrent. On the contrary, the soundscapes of the Stranger Things soundtrack represent everything we love about horror: They disorient us, force us to seek aural footing, and, as we get a better grasp on the implications of the Upside Down, reassure us that we will come out unscathed. And that process, as the success of the horror movie industry has confirmed, feels good.

“That, to me, is what horror films are all about,” Toop says. “At the end, almost always, a human being prevails.”

“What that’s saying is: You will survive yourself.”

Yasmin is a writer and former biologist living in New York. A Toronto girl at heart, her writing also appears in The Last Magazine and SciArt in America. You might recognize her as a past host of Scientific American's YouTube series.