Raise your hand if you’re still grossed out thinking about the Mind Flayer’s monster from Stranger Things season 3? It’s been almost a full month since the latest chapter hit Netflix and that disgusting, terrifying creature made out of exploded rats and body parts still haunts your nightmares. That’s understandable. But it turns out the real reason why that monster gave you the eeriest kind of chills is because it was inspired by the most horrifying idea known to humans: puberty!
The final episode of Netflix’s Behind the Scenes: Stranger Things 3 podcast is out now on all podcast streaming platforms and the half-hour installment is full of secrets from the Duffer Brothers and the show writers about the Mind Flayer and his revolting season 3 weapon made of Flayed people. But if you don’t have 30 minutes to spare, EW has rounded up all the biggest Easter egg reveals from the latest episode. (You can check out all the highlights from the first episode and all the highlights from the second episode, too.)
1. The demogorgons were always meant to be the appetizer. The main entree? The Mind Flayer’s monster.
“We always saw the demogorgons as sharks — the shark in Jaws — in season 1,” Ross Duffer says. “But ultimately, it was a creature. It was following blood. What we really wanted to do to up the stakes is create something sentient. That’s always even scarier to us than just a creature or a monster.”
And the Mind Flayer really is inspired from Dungeons and Dragons as he is on the show. “When we came across the Mind Flayer in Dungeons and Dragons mythology, it was such a shocking discovery,” writer Paul Dichter says.
2. The Mind Flayer possessing Billy was actually supposed to happen in season 2.
“We had actually spoken a lot about it in season 2 and that was something that I was very aware of, but I wasn’t really aware of how it was going to pan out,” Dacre Montgomery, who plays Billy, says. “Let’s talk about Jack Nicholson for a second. I feel like whether he’s playing the archetypal villain or hero or somewhere in between, he gives very unusual acting choices which I think keep the audience on their toes a little bit. That was a strategy I wanted to employ this season.”
Montgomery also researched dissociative identity disorder to portray Billy’s possession. “I did a lot of work in psychology on where the spot is, like which personality has control over the spot, the room, right? In your head,” he says. “The whole thing is the fight for Billy having the spot and having the voice. I did a lot of work [researching] people who suffer or live with those conditions.”
3. The Mind Flayer, trapped in the Upside Down, still needed a way to terrorize Hawkins in season 3. That’s why his creature was born.
“We got excited about [the fact that] he knew about Eleven now which he didn’t in season 2, which is really why we ended season 2 with the Mind Flayer hovering over Hawkins,” Ross Duffer explains. “Because now he’s aware that this girl has these powers that are extraordinarily strong and can stop him from his evil plans. We thought about the idea of him in that Hellraiser way of building a body.”
“We got really excited about going for it and building this season around some of this gross, body horror, Cronenberg stuff that we all secretly love or not secretly,” Dichter adds.
4. The Mind Flayer’s creature was inspired by John Carpenter’s The Thing.
“We wanted to do something fleshy this year and something with teeth and wet and heavy,” visual effects supervisor Paul Graff says. “I’m sort of the Mind Flayer’s uncle. I was part of his inception, not the very idea of it but the way he looks and developing it. So what would that look like if this Mind Flayer reincarnates itself in a creature that’s much more like a dinosaur or like a deformed dinosaur, like Frankenstein’s deformed dinosaur? It’s not a well-designed creature; it’s a thrown-together, nasty, weird body parts creature so it should be limping. Maybe some of those limbs you see are completely dysfunctional and it’s just dragging them behind him.”
5. But the biggest inspiration for the Mind Flayer’s creature was actually puberty. That’s why it’s made of so many awkward and gross body parts.
“Puberty is disgusting and it’s awful,” writer Kate Trefry says. “Let’s lean into that as much as we possibly can.”
Trefry always went back to caterpillars evolving into butterflies and how horrifying that process actually is. “I always thought they go into their cocoon, they grow wings, and they come out,” she says. “But that’s not what happens at all. When a caterpillar builds its chrysalis, its whole body dissolves into goo and then the DNA gets rearranged into a completely different animal and that animal is what gets reborn. Season 3 is this sticky, gross, toothy weird monster because it is that — it’s that moment of everybody is turned to jelly and we’re waiting on the edge of our seats to see what they become.”
For more on making the sounds, look, and movements of the Mind Flayer’s monster, how Eleven went into Billy’s memories, and where Billy’s trauma came from, the inspiration for Eleven losing her powers, Billy’s death, the firework finale scene, and more, listen to the full Behind the Scenes: Stranger Things 3 final podcast episode. Behind the Scenes: Stranger Things 3 is produced by Netflix and Pineapple St. Media. You can listen to it on Stitcher, Pocket Casts, Spotify, Google Play, iHeartRadio, and wherever else podcasts are available.