When J.A. Bayona calls and asks for something that seems impossible, David Martí and his team “are completely scared, but we say yes.” With a collaboration that stretches back to 2007’s breakout horror hit The Orphanage, the special effects makeup artist and the director have worked together so long that Bayona jokes, “David had hair the first time I met him.” And together they’ve jumped over and over into the unknown, bringing audiences into some of the most visceral, terrifying, and sometimes surprisingly emotional stories imaginable. “We normally don’t know how to do films before we do them,” Bayona says. “Because if we knew how to do them, we would never do them.”

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The challenge of Society of the Snow was pretty evident from the start. A rigorously accurate and passionate retelling of the crash of Uruguayan Air Force Flight 571 in 1972, the film required shooting dozens of actors in remote, snowy locations, and being as true as possible to the experience of the 16 people who managed to survive. “We cannot put fantasy or imagination on this,” Martí says. “It has to be real.” That required everything from filming partly at the real crash site in the Andes to handing the survivors human-body silhouettes on which to draw their exact injuries. Martí and his team were then tasked with meticulously recreating those injuries, including some that would never be seen in the film. “We did exactly what they had and then we decided how much to show it,” Bayona says. “It’s a movie about people taking care of each other. So they had to go through all of that so they could incorporate that into the performance.”

Below, Martí and Bayona break down five key makeup effects in the film, from subtle work to capture the extreme hunger endured by the survivors to astonishingly lifelike prosthetic legs. Society of the Snow is nominated for two Oscars, for best international feature as well as best makeup and hairstyling.

NANDO’S FACE

Though they would face many challenges during their 72 days stranded in the Andes, the survivors endured a wide range of injuries during the crash itself. Nando Parrado, one of several survivors who consulted on the film, hit the ceiling of the plane as it crashed, which left him with a swollen face and burst blood vessels in his eyes. For actor Agustín Pardella, that meant hours in the makeup chair, something experienced by all of his costars. “Agustín was always, always there with a good sense of humor,” says Martí. “He would come to the chair dancing.”

Martí and his team applied the blood and swelling to Pardella’s face as well as three different kinds of contact lenses for his eyes. As his injuries subsided, Parrado was left with what Martí calls “panda eyes,” referring to the black rings around them. As ever, adherence to the true story was key. “It was based on the reality of what they went through,” says Bayona, who notes that two other survivors were also key in remembering the extent of Parrado’s injuries. “We had the collaboration of Roberto Canessa and Gustavo Zerbino, who were studying medicine. They knew exactly what Nando had, and we were able to copy that.”

NUMA’S BACK

Of course, some of the most visceral injuries did not result from the plane crash at all. Numa Turcatti (Enzo Vogrincic), one of the film’s most significant characters, injured his leg and was stationary in the wreckage of the plane until his death 60 days after the crash. The result was these sores all along his back, which Martí says a doctor friend called “the most realistic wounds I have seen in movies.” But they’re glimpsed just briefly in the film, and only in the reflection of a mirror, in part to spare the audience. “We didn’t want to be too gross,” Bayona says. “We shot some things that I was like, Oh, my God, I cannot look at the screen if we see these kinds of things,” adds Martí.

One of those things was an infection in Turcatti’s injured ankle, an effect created by Martí and shot by Bayona, who ultimately cut from the final film because it was too intense. But much of Martí’s work, they say, was more for the benefit of the young and largely inexperienced actors. “You can see at the end of the film that the kids, they all went through the journey,” Martí says. “You will not see the wound on the screen, but you will see the wound on their faces.”

COCHE’S FACE

Martí credits the work of makeup designer Ana López- Puigcerver for the sunburn on Coche Inciarte (Simón Hempe), which required “washes and washes of different tones” to get right— “It’s actually like a painting,” he says. That color went on top of his work that added subtle facial and dental prosthetics to make Hempe’s face look more gaunt, capturing the extreme weight loss that all of the survivors endured. Martí sees this image as a tribute to the collaboration required to make the film possible. “It was something very impressive to see how many people can overlap work and make the same job for the screen,” he says.

“To me, it’s very difficult to separate the performance from makeup and hairstyle, because I think they go hand in hand,” Bayona adds. “This is why sometimes you will get, at the Oscars, the awards for the actor and the makeup at the same time—because it’s very difficult to separate.” Though the actors did lose weight as the production went on, there were limits, which is where Martí and his team’s prosthetics came in. “I think the actors knew a lot better where their characters were just by seeing themselves in the mirror,” Bayona says.

COCHE’S LEGS

Martí initially thought that these emaciated prosthetic legs would, like Turcatti’s infected ankle, be too visceral to make it into the final film. And like everything else, they were based entirely in the true story. When Inciarte arrived at the hospital with the other survivors, Bayona says, he weighed only about 55 pounds; as the director remembers, “He removed his pants for the first time in 72 days and discovered that his knees were very fat. And then the doctor said, ‘It’s not that your knees are big, it’s that your legs are very thin.’”

No actor could safely get legs that thin, of course, so Bayona enlisted Martí to build them; in the film, it’s a very simple effect of Hempe masking his real legs beneath the bed. According to Martí, the reveal has elicited gasps from audiences—“I’ve never gotten that in a movie I’ve done.” Martí and Bayona have worked together to create plenty of terrifying images over the years, from the haunting sack mask of The Orphanage to the many wounds of Society of the Snow, and Bayona has learned that the most deceptively simple images can be the most powerful. “You can relate to these thin legs,” he says. “You don’t want to make a gross film, but you really want to create an effect that will take [viewers] to the same emotions that [the survivors] went through. It’s an impossible journey, because it was hell for 72 days. But you can give little bits of that.”

GUSTAVO’S EARS

And then there were some prosthetics that had nothing to do with the ordeal of surviving in the Andes, but everything to do with honoring the crash’s victims and survivors. Playing Gustavo Zerbino, a survivor who went on to become the president of the Uruguayan Rugby Union, actor Tomás Wolf had to match one of Zerbino’s most distinctive characteristics: his ears. “He had a nickname—he was called Orejas, ‘big ears,’ by his colleagues,” Bayona explains. “So we had to do that.”

Martí was charged with making prosthetic ears for Wolf, who put them on daily in what was one of the simpler makeup jobs of the project. The challenge with him and all the other actors, though, was applying touch-ups during the scenes in which all of the survivors were gathered together in the cramped airplane fuselage, particularly when Bayona would track the camera past the face of each person. “J.A. doesn’t make it easy,” Marti says with affection.

With so much input from the real survivors, and so much effort put toward recreating their exact, harrowing circumstances, the cast and crew found the emotions of the story close to the surface almost every day. “There was a lot of crying on set,” Bayona says. “It was important for the actors to let [their tears] go and to create that safe space where they were able to try things. And sometimes some of these things were so unexpected and beautiful that you could turn around and see your DP crying in front of the monitor. The first time it’s kind of shocking, then there is a moment during the shoot that you get used to it.”

That even carried over to the Academy’s bake-off, in which seven-minute reels are screened to showcase the 10 films short-listed for the best-makeup-and-hairstyling award. Bayona himself edited the clip reel, and Marti said that he got emotional quickly while watching it in the room, comparing his reaction to what he experienced during the infamously weepy first 10 minutes of Up: “And then you have to go up on the stage and try to defend your work when your tears are still there.”