If you have yet to see last week’s episode ofGame of Thrones,“The Mountain and the Viper,” stop right now! In the words of the Viper himself, SPOILER ALERT.

We’re still collectively shuddering from Episode 8’s Oberyn Martell headsplosion and all the emotional implications it entailed. Because seriously,who wasn’t enamored with actor Pedro Pascal and his portrayal of the salty Dornishman? He left us too soon, but he also left us with a bang, and we’ve been wondering ever since exactly what went into the making of that fateful last look at Martell’s “face.”

We rang a couple of key folks behind the scenes to demystify the infamous moment. Turns out, it was a collaboration between the show’s practical-, special-, and digital-effects teams. Here’s what the evil geniuses responsible for all that carnage—visual-effects supervisorJoe Bauer and prosthetics supervisorBarrie Gower—had to say about how the shot (lovingly referred to during production as “the head squish”), ehem, gelled.

Joe Bauer: It was always intended to be a pretty nasty squish. We became involved during the edit. Alex Graves shot all the pieces and the prosthetic inserts and all that stuff and then cut it together, and then it became clear that—no matter how tight you cut it—if you go from somebody who is thrashing and writhing around to something that's static, which is the prosthetic head, they're never going to be continuous. So it became clear right away that we were going to need to join the prosthetic to the photography.

Barrie Gower: This is the first time ever that I've had to do a gag that is basically a crushable head that can be crushed in camera by another actor. We've done decapitations, heads that've been staved in with weapons, but we've never really done anything that would have an actor's hands have physical contact with the prop, and they crush it themselves. So we had to slightly rethink things.

Bauer: I know Barrie does extensive research, and we do as well. We need to see what the skin does, what the blood does, what gets crushed, what doesn't. It's all forensics and a lot of post-death trauma photography. It's horrible, it's the worst thing—and you have to go through, like, 50 grotesque shots that aren't the right thing before you get to the one that is. You never do that research close to bedtime!

Gower: It's very difficult with something like this as well to track down a man crushing another man's head, and what exactly it would look like. So it is partly artistic representation.

Gower: We took a mold of his [Pedro’s] head and we created a sculpture of his head with his eyes caved in, so the Mountain would be crushing his eyes in. And we did another of the head, which had him sort of grimacing and some of his teeth missing. And we created a silicone rubber skin on the head, which is breakable, and it had internal gore, so it had a shell inside and it had lots of brains and we put blood tubing and all kinds of things inside it.

Bauer: You'll be amazed at how much testing went into it. . . . I was at his [Gower’s] facility in London, and the whole parking lot was covered in fake blood. People driving by who didn't know what was going on kept slowing down because they thought something really horrible had happened.

Gower: We had to be very careful with the heads when transporting them, because they were built in London and shipped out to Croatia. And that was a terrifying 24 hours while those were shipping out there. We shipped three heads. We could only complete the heads to a certain point—so they were fully artworked, they were painted and they had hair on them and they had eyebrows and they had stubble. But the interior of them we had to prep when we got to Croatia, because we had to fill them with blood bags and various other things. And if we did it prior to traveling, the weight and the disturbance of traveling would split the heads, basically.

Gower: For [the inside of] Oberyn's head we used various foams. Theatrical blood mostly contains water, food coloring, syrup, sugar—and by mixing that in with some of these polyurethane foams . . . it creates very strange shapes. We made blocks of what we call “nurnies,” which are basically silicone to look like brain matter and what have you. We made lots of strips of latex, strips of silicone, all kinds of different things to look like brains. And then you cover it in blood and it just gives you lots of lovely little shapes.

Gower: We actually had several elements, as far as the gag went. Our first involvement with the scene would be when Oberyn trips over and the Mountain grabs him and punches his teeth out. We had made several separate dentures to be thrown across the floor, which Alex Graves, the director himself, actually threw across the floor when they filmed it.

Bauer: We had to paint a lot of Pedro's teeth out [in post-production], because The Mountain was supposed to have smashed them out.

Gower: We cut to the actor, he was lying down, and the effects department . . . they had several little blood tubes and various gags which they actually put inside Hafþór’s [the Mountain] hands, up into his thumbs, so it could pump blood around Pedro's actual eyes—and he had protection around his eyes.

Bauer: We had to make C.G. thumbs that would stay in the eyes, because the actor playing the Mountain [Hafþór Júlíus Björnsson] was so cautious about getting his thumbs near Pedro's eyes, that they were always hovering over the top, so we had to get the thumbs really dug far into the prosthetic.

Bauer: The final shot, where we really see his destroyed face, was something that we did a number of variations on, and it really came down to getting his bottom jaw out of alignment with the rest of his skull, which was just a Photoshop treatment, and then I did it for real in 3-D. If you really watch the sequence, it's some really quick and clever cutting and a couple of shots where we split the actor, Pedro's, face. So from the nose down it's the actor, and from the nose up it's the prosthetic.

Bauer: The squish actually was in camera. It's like two or three quick cuts—the one with Peter Dinklage in the background, and then the top shot with the camera rising up as the Mountain rolls off of him and you see what happened.

Gower: It was a huge sequence from a practical effects sense. And then the [digital] effects team came in and added these lovely little shapes—bits of jaw, bits of nose, bits of skull, I mean really grotesque. So immediately you could clock what part was the face, because it was quite—it was disgusting, what we did on the day.

Bauer: We completely replaced his [Pascal’s] head and the blood around his head—you see the blood spreading out. We added the brain matter off to one side and then added his face features, although mangled, we added them back over. They had shot a dummy with a bunch of just meat where the face was, but it was too mangled to the point where you questioned what you were seeing rather than understanding it right away.

Gower: The first time we'd all seen it cut together, everybody winced—you just got the perfect reaction. I loved it. I saw it in Belfast about a month ago, and it was with all the heads of the departments, and they put this reel together of highlights of Season 4. And so there's a room of about 40 of us, and the reaction was brilliant. We knew what to expect, but seeing it all cut together with the audio and the reactions of the actors—it was perfect, absolutely perfect.

Bauer: Even having worked on it, I feel horrible that it happened!

For those of you willing to relive the moment,it's viewable here. Or this quick glimpse might be enough:

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Watch: Pedro Pascal Weighs in on … [SPOILER ALERT]