Matt and Ross Duffer (Wayward Pines) are taking EW behind the scenes of every single episode in their thrilling new Netflix drama, Stranger Things, an ’80s-set supernatural show starring Winona Ryder and a slew of fantastic young stars. (Catch up by reading EW’s season 1 recaps.) Here, they dive into “Chapter 6: The Monster”…

For a chapter titled “The Monster,” it’s actually very light on, well, monsters. At least monsters of the supernatural sort; bullies and jealous boyfriends are another matter. But we’ll use our chapter title as an excuse to satisfy our inner child and talk about our actual monster.

It has always been something of a lifelong dream to create a monster and bring it to life on-screen. Not in the computer, but for real. To build it. Like so many filmmakers our age and older, we grew up on genre films that existed before computer graphics. There was something about the effects being so tangible in those films that made them especially terrifying to us when we were kids. We’re specifically thinking about Ridley Scott’s Alien, John Carpenter’s The Thing, and Clive Barker’s Hellraiser. So from very early on we knew we wanted to build an animatronic monster.

First, we had to design it. We hired Aaron Sims, a wonderful concept artist, to help us construct our monster. We spoke to him at length about the creature designs of H.R. Giger, Clive Barker, Guillermo del Toro, and Masahiro Ito (Silent Hill). We all felt their monsters were so effective because of their strangeness. If you were to encounter a being from another planet or dimension, we imagine it wouldn’t look like anything you’d expect. The more bizarre, the more frightening. Eventually, we landed on the design you see in the show: An unnaturally thin monster with no face, long arms, and a head that opens up like a disgusting flower when it’s feeding time.

The next step was to build it. We decided to work with a company called Spectral Motion. Spectral did a lot of work on Guillermo del Toro’s Hellboy films and they’re one of the most experienced companies with animatronics. It was a race to get the creature completed in time; they had only about two months, meaning there was almost no room for error. But they knocked it out of the park. The first time we saw our monster’s head peel open… it just blew our minds and transported us back to our childhood. And the way it moved was terrifying — their brilliant robotics engineer had designed the animatronics in such a way that the movement of the head “petals” never repeated themselves. They had a life of their own, moving in unpredictable and bizarre patterns. It felt organic. Creepy. Real.

We loved it, and so did the actors. Well… not all of them. There were some toddlers on set: Millie’s little sister, Ava, as well as Anniston and Tinsley, the twins who play toddler Holly. As you can expect, these little girls were all terrified by the monster. Finally someone had the clever idea to tell them that the monster was not a bad monster at all; rather, he came from world of Monstropolis in Monsters, Inc. And it worked! The monster wasn’t scary to them anymore, he was a friend! This was even more satisfying given that Millie’s little sister looks and behaves exactly like Boo.

Of course, sometimes we needed our monster to do something that a man in a suit feasibly couldn’t do (e.g., breaking through interdimensional walls). For this, we turned to our amazing team of visual effects artists. Luckily, our monster concept artist Aaron Sims also runs a small VFX company (ASC), and we put them in charge of all of the monster CG shots. No one cared more about this monster than Aaron — it was his baby. We think his passion shows in his work. He and his team did a remarkable job. You’ll see much more of their work in the final episode, although we hope you won’t be able to tell what is CG and what is practical — we hope that it all just feels real.

Now you know how we made the monster, but there’s still a lot of mystery concerning what it is. We don’t want to reveal much, other than to say it is an interdimensional being that has more in common with the shark from Jaws than Pennywise from It. When the monster enters our dimension, it’s like a shark breaching the water. Very much like a shark, it drags its prey back into its home, where it feeds. Each time it enters our world, it leaves a small tear, or wound. That’s what Joyce found in her wall in episode 4, and Nancy found in the tree in episode 5. These tears are almost like portholes into the Upside Down. But they don’t last very long. Like wounds, they eventually heal and seal up.

We don’t want to tell you much more because we want everyone to experience this story from the point-of-view of our characters. After this episode, hopefully you know just enough: That touching an interdimensional being is never a good idea, that the monster is drawn by blood, that it hunts alone, and that you should probably stay away from it. Unless, of course, you want to find it. Or kill it…

Random trivia: It was Caleb’s (rather insistent!) request that Lucas wear a camouflage bandana in the show. He wears it for the final three episodes. Sometimes our kids have great ideas, and this is one of those times!