[creepy music] (host) You never see it coming.

In fact, you never see it at all.

In the shadowy corners of 19th century America, deep within the forest, lumberjacks spun tails of an incredibly dangerous creature living in the woods of North America.

What it looks like, no one knows.

These monstrous animals lurk behind the tree trunks, never revealing their true form until it's too late.

It has an uncanny ability to shield itself from human view, but that doesn't mean it isn't there, silently stalking you through the trees, always lurking just out of sight, always watching, always waiting.

They called it the Hidebehind.

The Hidebehind is a uniquely American creation, but it belongs to a much older, broader tradition of unseen monsters.

And after all, what's more terrifying than a monster you can't escape, one you can't see, or shouldn't see?

Across cultures and centuries, humans have imagined invisible threats that stalk them.

The unseen monster exists in many forms, and it's far more widespread than you think.

[mysterious music] The Hidebehind was a piece of folklore that spread among lumberjack camps, especially those working in the dense, isolated forests of the Pacific Northwest.

Logging was one of the most dangerous jobs in the 19th century.

Men worked long hours, and accidents were frequent.

When someone went missing, it made for a perfect setting to tell the tail of the Hidebehind.

Lumber camps were essentially tiny social ecosystems.

Brought together by career and isolated in one place, bonds were quickly drawn to establish familiarity, and what better way to do that than with a scary story?

Storytelling was an essential component for lumberjack camps.

With exhausted bodies and not much else to do than eat, drink, and sleep before the next hard day of work, before heading to the bunkhouse, it was tradition that all would gather around the fire to hear a good yarn, many of which were told as a sort of indoctrination to newcomers.

Some old timers would even hide behind trees and make animal noises to try and scare the rookies.

The best storyteller at the camp would occupy the deacon's seat, a place of reverence and authority.

But many of these stories, just like those of the Hidebehind, weren't just entertainment.

They were explanations.

While a true description of the Hidebehind is impossible given its nature, many stories say that it is just under six feet tall with long, shaggy hair covering its body, making it difficult to distinguish any features.

While others say the Hidebehind takes on a more shadowy, nebulous form.

Some say it is an ancient animal from prehistoric times that lingers in the woods to this day.

What is agreed upon is that it stands upright like a human.

Clawed, unusual footprints mark its presence.

It pounces upon its victims from behind before dragging its prey into a hidden layer to feast upon the remains in peace.

The favorite meal of the Hidebehind is human offal, specifically, the intestines and colon.

When their meal is particularly tasty, they are said to laugh and delight.

The surefire way to protect yourself from the Hidebehind?

A little booze.

That's right: even a single alcoholic drink would deter the Hidebehind from eating you, but not from attacking you.

They need to smell the alcohol on your intestines first.

So, presumably, if you drank enough, no disemboweling would be required.

Loggers work from dawn to dusk, swinging axes and hauling heavy timber through dense, remote forests.

Outside of human error, you had to worry about cold temperatures, wild animals, and the simple unpredictability of nature.

Accidents were common, and when someone went missing, there weren't many readily available options to explain it all away.

So the Hidebehind was blamed for the vanishings of woodsmen who wandered too far alone or who met an unfortunate end.

Stories of the Hidebehind help make sense of loss, isolation, and the unpredictable dangers of the wilderness, and maybe even the brutality of other humans.

I'm not saying that someone was out there disemboweling folks left and right, but I'm also saying it's not impossible.

The Hidebehind is a uniquely American creation, a monster born from the tall tales of hardworking lumberjacks looking for an excuse to tip one back after a long day.

But its roots reach deeper into a much older tradition, the fear of what we can't see.

Across cultures, stories abound of invisible beings that torment people.

In Inuit tradition, the Tariaksuq, or shadow people, are always around, but just out of sight.

You can hear them talking and walking, but see little more than a dark shape.

They're said to move between our world and their realm.

Shy beings, they aren't inherently nefarious, but they are shrouded in warnings.

You should never look directly at them, even if you sense them watching you.

Some stories even claim the trickier ones will try to lure you into their realm and hold you hostage.

In Hawaii, the Nightmarchers are one of the island's most famous and deeply respected legends.

They're not monsters in the Western sense, but are said to be spectral warriors who march unseen, punishing those who dare to watch them.

Witnesses describe sights such as a line of torches flickering in the dark, along with sounds of conch shells, chanting, drums, and marching feet.

Encounters with Nightmarchers are deadly serious in Hawaiian tradition.

You should never look at them, and lie flat on the ground, face down, to show respect and submission.

Otherwise, you'll be killed, struck by a spear, or simply found lifeless the next morning.

But perhaps the most famous unseen monsters are poltergeists.

Poltergeists are said to mark their presence known through noises.

In fact, the word itself comes from German, poltern, to make noise, and geist, spirit.

Literally, noisy ghost.

The word first appeared in written form around the 1500s, describing noisy, mischievous hauntings in German speaking regions.

Poltergeists are known for general chaos.

Objects break or are thrown by an invisible force.

People report being scratched, pushed, or grabbed by something unseen.

Not being able to hide from a monster or having a chance at defeating it is scary enough, but not even being able to know what or who the threat is?

That's truly terrifying.

These stories feed on uncertainty, exploiting the dark spaces between what we know and what we fear might be true.

All of these unseen monsters, when we stop trying to decide if they're real or not, tell us something interesting about the human mind.

We're constantly scanning the world, looking for patterns to help us determine what's safe and what's dangerous.

When information is missing, the brain tries to fill in the blanks, and when it comes to potential threats, it assumes the worst.

We have evolved to pick up on cues that may be seen as threatening or dangerous and respond quickly and accordingly.

In fact, scientific evidence supports that we are literally hardwired to process a scared face faster than a happy one, so when we can't even see the body of the monster, let alone its face, yeah, we're gonna have a visceral response.

This is known as the better-safe-than-sorry bias, which basically boils down to a survival mechanism.

It's a conservative bias in our brains that tells us not to wait around and find out.

What some might call an irrational fear, others will point to as preventative risk avoidance.

Our brains have evolved to recognize and respond to environmental threats.

It's literally what has helped us survive as a species.

But what if we sense there is a threat and we can't see it?

When we prepare our bodies for the fight-or-flight response, our pulse rises, energy is dispersed into our muscles, and our senses sharpen.

This happens even when the threat is imagined.

Our brains can detect subtle changes in the environment.

Maybe the temperature drops suddenly by a few degrees, or an unseen animal makes a noise.

Our brains turn this into the presence of a ghost, perhaps.

Horror and folklore involving monsters you can't see, like the Hidebehind, exploit this instinct.

That's the genius and terror of unseen creatures.

They're embodiments of uncertainty itself.

Filmmakers have tapped into this primal response to amp up the fear factor.

"Jaws" might be one of the greatest examples of: what you don't see can be more terrifying than what you do.

For most of the film, the shark is barely shown.

The mechanical monster broke down constantly, forcing director Steven Spielberg to suggest its presence rather than outright showing it.

It's that incredibly effective opening attack sequence.

You never see the shark, only a woman thrashing, dragged under, and the water calming again.

The terror is psychological.

Also, in "Alien," your imagination does most of the work.

You see glimpses of the spider-like Facehuggers and the freshly born little baby Xenomorph, but you don't see the full grown alien until roughly around the halfway mark.

[crew member screams] The ship is dark and claustrophobic, and the flickering lights make it hard to see exactly what you are looking at, if anything.

(character) What?

(character 2) There's all kinds of stuff down here!

(character 1) What kind of stuff?

(Emily) "The Blair Witch Project" is one of the purest forms of the unseen monster.

In the infamous found-footage movie, three film students investigate a local Maryland legend.

They hike through the woods in search of the famous witch, tormented by something unseen.

(character 2) I'm going upstairs!

(Emily) Every bit of fear comes from what's implied, and evidence the terrorizer leaves for the filmmakers to find, including some really creepy stick doll effigies.

Spoiler alert: what's ever haunting those woods never reveals itself.

Not once.

But there's more to it than fear of the unknown.

These monsters are inside us, in the way our minds work, in the stories we tell to explain what we don't understand.

And if monsters are representations of what we believe to be undesirable in some respects, then an unseen monster speaks to our own anxieties of loneliness.

The unseen monster is the shadow of our imagination, proof that our greatest fears don't always need form or face.

But as long as there are dark forests, literal or metaphorical, there will always be something hiding behind the trees just out of sight.

So, is that bump in the night really a monster, or just your mind turning uncertainty into a story?

In fact, you never see it at all.

-In the shadow-- -(crew) Can you peek out more?

Yes!

Okay.

The Facehuggers come from the eggs.

The Facehuggers then lay an additional egg, and then that is birthed.

That is standard practice.

Standard alien practice.

Little baby Xenomorph.

Ding!