A little boy sits alone on the floor of his bedroom. Backlit by a window, he leans over pages of construction paper on which he is obsessively drawing. A platoon of little green Army men guards the pages, and ultimately the boy. As the camera pans around him, he does not speak — in fact he has not spoken at all since his father drowned in a local lake the year before.

This is not the first time the audience, or even the main characters of “Supernatural” are introduced to this boy, as the moment comes a little less than half-way through the third episode of the series. But through the scene setup and shot style, it is the first time the audience gets a glimpse of the boy’s psyche, which will prove to be indispensable as the Winchester brothers work to solve the case of the mysterious lake deaths. It is also a turning point for a first-season show that would eventually run for 15 years.

“I watched Kim [Manners, director] set up this one shot and I thought, ‘That’s the way the show should be shot. This is the look we should be going for,'” executive producer Bob Singer tells Variety.

Creator Eric Kripke originally pitched “Supernatural” to studio Warner Bros. and eventually then-network the WB as a monster-movie-of-the-week drama about two brothers (Dean and Sam Winchester) who travel the backroads of America hunting the things the audience would remember from urban legends. But his main goal in his original pitch document was that “the weekly stories have to be SCARY AS S—.” (And yes, the all-caps was his emphasis.)

While he wanted to make “this series as scary as I can,” he wrote at the time, not all fear comes from an external source. Soon enough, it was the characters’ own trauma and internal struggles that were driving story and adding rich complications to an already well-known genre.

“We set out to make a horror show, and those were the initial stories we wrote. But you learn and adjust as you start watching the film, and a few things conspired to tell us, ‘We have to focus a lot more on the characters than we’re currently doing,’ which is we realized the actors we had,” Kripke tells Variety now. “We saw that they were just both wildly charismatic and emotional and were knocking everything we gave them out of the park. So we were like, ‘We should start giving them harder things to do because they can handle it.'”

The pilot introduced Dean (Jensen Ackles) and Sam’s (Jared Padalecki) trauma briefly, first by revealing that their mother died under mysterious circumstances in a house fire, resulting in their father devoting his life to hunting what killed her — even when it meant dragging his school-aged kids on the road and leaving them alone for days on end in rundown motels. When Sam’s girlfriend dies in a similar way in the present-day portion of the episode, a deeper, psychologically-scarring mythology is hinted at — but the focus of the first few episodes of the series is really more on the “task at hand” of taking out whatever creature is right in front of them — from a Woman in White in the pilot, to a wendigo in the second episode and a ghost in the third.

“When you get hired as staff on a first season show, you get handed the documents they used to sell the show, and that included some of the family secrets and what was going on with Sam. But it’s more like it was a headline that these children had been through a lot because of, we’ll call it, their unconventional life — and the details come when you start to have more space to tell the story,” says Sera Gamble, who penned “Dead in the Water,” the pivotal third episode of the first season with Raelle Tucker, and later went on to run the show in the sixth and seventh seasons.

When breaking the story for “Dead in the Water,” Gamble recalls a conversation with Kripke about how “most young children, especially who have been through something, [are] not just going to open up and give you all of the procedural information you need as an [exposition] dump in the scene.” In discussing how it needed to be harder to draw information out of that child, Gamble says she was inspired to “dig deeper into the psychology of the characters in that script,” which became a baseline for episodes going forward.

“Now I can’t imagine approaching anything with a fantasy element without starting from that place,” she says. “These stories were scary to us because they feel like they tap into something true. Your road as a writer to something that’s going to terrify the audience is through human psychology.”

What each audience member finds scary can vary — and often comes from factors outside a show’s control, from the person’s own upbringing and experiences to the kinds of other stories they consume. In order to to make sure to deliver unique horror elements in each episode, Singer says that from the beginning, “one thing we always said was that the shooting style should be commensurate with what the monster was or what the tone was, so we didn’t feel like we were doing a cookie-cutter horror [show].”

The characters within each of those episodes also had to be unique, even if the type of creature the Winchesters were fighting was something they’d encountered before. “Halfway through Season 1, the first run of the scripts, we realized we were going to run out of monsters in a hurry,” if we didn’t, Singer says. “So if we did a vampire story, each version would not be what you’ve seen before — each version had their own story.”

Often these characters had traumatic backstories of their own, such as Gordon (Sterling K. Brown), a hunter who was on a one-track mission to eradicate the supernatural from Earth after his sister was taken by a vampire when he was just a teenager. (In the most heart-wrenching twist, he later was turned into the thing he hated the most.) Sometimes they even brought out complicated issues for the main characters, such as when Sam fell for Madison (Emmanuelle Vaugier), a werewolf who he was going to have to kill, reigniting the fears he had about losing the women he loved.

And as time went on, those issues and fears began to pile up and often go unresolved. Dean never truly mourned his mother and Sam didn’t fully get to grieve his college girlfriend Jess (Adrianne Palicki) and both had complex feelings about their father and the way they were raised. But then Dean traded his life to save Sam’s, sending the older Winchester to Hell (literally), while the younger one had to carry on alone. Being the true vessels for Michael and Lucifer could have pitted the brothers against each other but ultimately this time it was Sam who went into the pit to Hell, leaving Dean to move on. Sam also lost his soul, got addicted to demon blood and never quite could shake his PTSD from his time with Lucifer (Mark Pellegrino); Dean ended up with PTSD after getting back from war-like Purgatory. Both brothers struggled with wanting to believe in Team Free Will, even when learning they are literally God’s (Rob Benedict) favorite television show and their lives have been manipulated for it. And of course along the way they’ve lost countless other friends and loved ones, from surrogate uncle Bobby (Jim Beaver) to Charlie (Felicia Day) and even their mother (Samantha Smith) again after she was brought back from the dead, only to eventually be killed by Lucifer’s son Jack (Alex Calvert).

“Sam and Dean both went through a ton of trauma. Sam probably had more reminders of his trauma because, obviously Pellegrino remained as Lucifer for many, many years, and Sam had to be facing his No. 1 offender in causing his PTSD,” says Padalecki. “The writers, obviously, always were aware that Sam had been through what he’d been through with Lucifer so they peppered that in [but they] allowed me to take it further if I needed to.”

While Kripke acknowledges that the broadcast format — especially back in 2005 — lent itself well to a slow burn on mythology in the beginning, he also believes characters are more interesting if you “peel back those layers one at a time” as the show goes on. But there is also a more pragmatic reason behind easing the audience into the more psychological horror of “Supernatural” according to Dr. Lynn S. Zubernis, a licensed clinical psychologist, professor and author of several “Supernatural” books, including this year’s “There’ll Be Peace When You Are Done: Actors and Fans Celebrate the Legacy of Supernatural.”

She explains: “One of the reasons that we as humans have so much trouble processing trauma is that we literally store those trauma memories in a different way to store our regular memories and then we can’t get to them and they just end up split off and unprocessed and we don’t want to go there. So we have a lot of defenses against looking at our own trauma. That’s why projecting onto fictional characters is such a great way to do it. But if it came at us all at once, our brains would be like, ‘No, no, no no; we’re not going there.’ You have to go slow in the beginning and then be hooked in and trust the storytelling, in a way, before it goes that deep.”

The same was true for the actors. “Early on, we maybe had to use some techniques or some tricks of the trade to get to a certain point emotionally, but as time went on and the seasons went on, we didn’t have to use those tricks,” says Ackles. “Living with this story — not just living with the characters but living with this story — when things happen, we’re able to really feel it from a character’s perspective because we have lived with it so long and we understand their hurt and their pain and their laughter and their joy.”

Adds Padalecki: “We lost so many characters, I feel like we had a lot of chances to deal with what Sam and Dean would go through with the loss of a character or friend, and so, after the 30th time, it was like, ‘OK I remember what Sam goes through; I remember how he feels; I remember how to be and where I want to be in the storyline as a whole.’ If God forbid there came a situation where they were like, ‘Hey we need to shoot this scene tonight, it’s two pages, it’s you and Dean and Lucifer, then I could have done it — and Mark and Jensen could have done it as well.'”

As the show evolved, the type of horror it delivered week after week would consist different ratios of a combination of jump scares and more of a “disturbing fear that doesn’t leave you — the kind of fear that gives me chills, instead of making me want to scream,” as Zubernis puts it.

“I remember getting a note from Eric that changed the way I wrote the show and kind of cracked the show open for me,” Gamble says. “It was [for] an episode where a demon in the body of a woman has, I want to say, Bobby tied up and they are snarky back and forth but he is her prisoner. And what Eric said was, ‘You’re writing these lines where the demon is very witty and funny and smart, but the thing that is so terrifying about a demon, even as you are entertained by it is that they can see straight into your soul.’ So this thing that they will say to you will be the thing that hurts the most. And so, that was the guiding principle for writing the bad guys: They had to be incredibly insightful to find these guys’ Achilles heels.

“It was also the guiding principle in writing Dean, who was very much going to say the funniest lines in episodes, but he’s never trying to crack you up — he’s actually speaking from a deep well of pain and his way of processing that is to say something hilarious like he’s tough and it doesn’t matter,” Gamble continues.

“We knew the guys had deep trauma and deep pain and were frequently struggling quietly with something, and we always held the monster peril or the danger to a high standard of, ‘We’re not going to make this a joke. This is going to really be life or death.’ So if you have those pieces of the puzzle where the life or death stakes are there, the emotional truth is there, and then you have characters who crack a joke in the face of death, then you can go a lot of places tonally.”

This included expanding the world out to get inside the heads of other core characters — from Castiel’s (Misha Collins) own struggle with how he allowed power to corrupt him, to Jack’s guilt over killing Mary, to diving into memories of Bobby losing his wife and Jody Mills (Kim Rhodes) losing her own family. In some cases, it meant quite literally spending the majority of episodes inside characters’ heads, as well — from Season 2’s “What Is and What Should Never Be,” in which Dean’s psyche is in an “apple pie” alternate reality while he is losing his life to a djnn, to Season 4’s “The Rapture” when Sam is detoxing from demon blood, to Season 7’s “Death’s Door,” which sees a dying Bobby trying to outrun his reaper.

In the latter episode, Gamble reminds, the show was “exploring his core wounds by seeing the memories that are the most important to him.”

“We observed from just watching so many shows in this genre that the Big Bad gets bigger and bigger every season and the war gets more massive and pretty soon you’re a tiny little Lego guy and you’re literally facing God,” she explains. “So part of our job from very early on was to slow down or to avoid running into plot that was so massive that you’re just little specs in a giant galaxy. The way to approach that is always to come from what is personal inside of the story to the boys.”

After all, at the core of the show was always the Winchesters — whether the danger they were in was because of a literal demon in front of them or an internal demon they had yet to conquer.

“If you put them in real jeopardy — believable jeopardy for our world — then the scares will take care of themselves,” Singer says.

(Pictured: Jensen Ackles and Jared Padalecki in “Supernatural,” which returns with its final seven episodes beginning Oct. 8 on the CW)