Rachel Weisz is beside herself. The emotional volatility that the new Dead Ringers TV series demanded of her would push any actor’s limits, but the show was twice as harrowing since she’s playing twins. Weisz stars not only as the manipulative, ethically challenged fertility doctor Elliot Mantle, but also her overwrought, emotionally fractured twin, Beverly.

The series, now streaming on Amazon Prime, is an adaptation of the 1988 David Cronenberg movie of the same name, which starred Jeremy Irons in the dual roles. Both projects are fictional takes on the 1977 novel Twins, which chronicled the rise and fall of two brothers whose genius as medical practitioners was undermined by their self-destructive appetites. 

Throughout the show, Weisz appears to seamlessly interact with herself, but on set she acted both sides of the role opposite Kitty Hawthorne, who gave Weisz both a physical presence and the emotional pushback necessary for her to create the disparate halves of each scene. Hawthorne, known primarily for stage work, does make her onscreen debut in the show as the twins’ mother, but most of her work on Dead Ringers was painted over in postproduction by the performances she helped Weisz bring to life. “We had to find someone who was really good and at that point in their career where they were willing to be the sort of invisible hero,” codirector Sean Durkin says.

Although Hawthorne and Weisz don’t look alike, sometimes Hawthorne would stand in as one of the twins for over-the-shoulder shots of the Mantle sisters in conversation. That’s a tried-and-true Hollywood twin technique, and Alice Birch, the creator and showrunner of the series, recalled combing through each scene with the VFX team to adjust tiny details. “I think I can tell the difference between the back of Kitty’s ears and Rachel’s now,” she says. “What an extraordinary and useless skill!”

Appropriately, the challenge of believably doubling Weisz often required a two-pronged approach, old and new. Visual effects have obviously evolved over the three decades since Cronenberg cloned Irons onscreen, but for all the state-of-the-art tools, like the facial replacement of deepfakes and photo-real digital animation to generate object handoffs, the Dead Ringers TV show also often deployed comically primitive tricks that were just as good at fooling the eye.

“We did a couple of silly gags,” VFX supervisor Eric Pascarelli says. “If they were touching each other’s face, we just put their elbows down under the bottom of the screen and used Kitty’s hand.” Then Weisz’s performance of the caressing twin would be subbed in for Hawthorne’s body, while that hand reaching up from below screen remained onscreen, touching the face of the other side of the performance. To make it perfect, digital artists painted Hawthorne’s skin with the textures of Weisz’s own hand. 

“There were a couple shots where we pulled, I’m going to say, ‘cheap’ gags like that, but they were very effective,” Pascarelli says

Lone actors have been doubling as twins since the dawn of moviemaking, with early filmmakers experimenting with the double-exposure technique frequently used to generate “ghost” imagery. In this process, film is simply exposed twice, creating two impressions on a single finished image.  

One of the earliest professional examples of twin creations was the 1912 adaptation of the Alexandre Dumas novel The Corsican Brothers, starring George Lessey as two men who were once conjoined and can still feel each other’s emotional state. Then both fall in love with the same woman. To generate his performance, one half of the frame would be masked while he shot the first part of the performance, then the covered sides would be switched as he performed the other. 

The ability to interact continued to evolve. By 1921, Mary Pickford could lean in and kiss a version of herself on the cheek in Little Lord Fauntleroy. (In this story, she played a mother and daughter, however, not twins.)

Since then, actors who have played twins include Hayley Mills as sisters in 1961’s The Parent Trap, who conspire to reunite the girls’ estranged mother and father. This used a state-of-the-art optical printer to create a more advanced version of the split-screen effect. A double was sometimes used for over-the-shoulder shots that suggested the identical girls were in the same scene together, but otherwise the filmmakers looked for innovative ways to hide the dividing line. The technique moved to TV two years later with Patty Duke playing the genetically unlikely “identical cousins” of 1963’s The Patty Duke Show.

More recently, Mark Ruffalo played twins in I Know This Much Is True, which Pascarelli also worked on as a VFX supervisor before Dead Ringers. While Weisz would shoot her sides as Beverly and Elliot within the same day, Ruffalo’s performance was more protracted because his twins were not supposed to physically match each other. “They were both Mark Ruffalo, but he had to gain 30 pounds or so,” Pascarelli says. “So we had to separate the shooting of the two twins by six weeks.” The upside was that one performance was entirely finished and could be matched more easily.

Dead Ringers benefited from more than a century of twins on film, and many of the old techniques still work, albeit merged with new ways to hide the transitions.

Birch refers to this innovative fusion of old and new techniques as “hacks,” and without them, Weisz’s performance as the Mantle twins would be nowhere near as creepy. Her twin doctors are almost pathologically inappropriate—heedless in their professional work, and disturbing in their private lives. 

“I think the intimacy, for sure, is a little troubling. It’s creepy,” Birch says. “It gives [the show] much of its very strange kind of slippery tone. But particularly at the beginning, it’s setting up the stakes.” The twins are engaged in various acts of seduction—sometimes with wealthy benefactors whose money they need for their clinic, and sometimes with patients they prey on as romantic partners. All of these bad decisions begin to weigh on the troubled sisters. 

Birch felt she had to establish their unsettling closeness—which wouldn’t have been the same if the viewers weren’t convinced of the doubling trick. “Codependence feels like much too small a word to show what’s going on there,” Birch says. “They’d been completely close, and completely intertwined, and [meant] everything to one another. Then, hopefully, we’ll really feel that rupture and divide.”

Birch and her writing team first imagined the story with zero constraints, writing interactions between Beverly and Elliot as if they could easily be performed by two separate actors. “I didn’t think about the technical side at all, which, looking back, feels mad,” Birch says. “In the writers room we talked about how we wanted them to be as close as possible, and that they would be in the same frame as much as possible, and there’s physical contact.”

Only later, in preproduction, did they confront the limitations, and the never-ending question of how to accomplish each interaction. “No matter how much knowledge you had about how to do twins, each scene created its own scenario where you would have to come up with something new or some new way of doing it,” Durkin says.

Birch would then work with the director on the script to decide if each interactive moment was worth the trouble—and the budget. “Sean might make the first initial suggestions: ‘In order to get that scene, we might have to lose this scene,’” she says. “Or ‘Can we have the same feeling without them being physically close or without them being in the same frame?’” Then the VFX chief weighed in. “It might go through another stage where Eric’s like, ‘We’re going to need three more shooting dates for this episode in order to pull that off. So can you make the cuts…?’” she says. “It was a slow sort of whittling down.”

Part of the thrill of a show like Dead Ringers is the magic of Weisz appearing to do the impossible. “I would say for the most part, because Eric and his team are so extraordinary, he was always trying to find a way to solve it rather than saying, ‘cut,’” Birch says.

One such moment features Weisz in an elevator as the two grown sisters engage in a comically juvenile slap fight. “We were trying to tell a lot of story in quite a silly, sweet, strange exchange,” Birch says. “We were interested in them being able to revert to children. The technical side of that was very, very complicated for such little screen time, but I’m really pleased we kept it.”

Pascarelli breaks down the “hacks” this way: “I said, ‘Here’s what we’re going to do. She’s wearing a sweater over her shoulders and it’s a black sweater, so we actually used Kitty’s arm from the black sweater on.’ Since the black sweater was so dark, it was a nice place to slice the image right there.”

On the other side of that splice, the VFX team would substitute Weisz’s body for Hawthorne’s. But the twin characters’ torsos had to remain steady for it to work, so Weisz played it like the feuding sisters could barely tolerate looking at each other. “We just made sure that she didn’t move around. They were leaning against the wall and then they stayed fixed against the wall,” Pascarelli says. “So we try to limit ourselves in ways that people aren’t really noticing.”

Then in postproduction, his simple fix hit a snag. “The best performance happened to be one take where the sweater slipped off of Kitty in the middle. So there was a lot of work to fix that shot. They cloned the sweater from earlier in the scene and “froze it,” Pascarelli says. “Also, she was wearing a very shiny shirt and so we had to work around that. It was difficult. But obviously it worked.”