Following is the transcript of the video.

Narrator: Take a look at this scene in 1961's "The Parent Trap." It's pretty easy to spot where the shot is stitched together to make it look like Hayley Mills is playing two twins.

Now take a look at this shot from the 2019 movie "Us." Lupita Nyong'o appears to be head-to-head with her doppelgänger, who's clutching her neck as they grab each other by the wrists. To pull off this scene, director Jordan Peele needed much more than a simple stitch.

But creating complex twin shots like this one required a lot of building blocks over more than 100 years of innovation. So, how did it happen?

Having one actor star in dual roles was a popular novelty in the silent-film era and in the early talkies.

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See this shot from 1898, where the illusionist Georges Méliès created four moving versions of his head in one frame? It was accomplished with the use of matte shots, which were kind of like old-school green-screen composites created by blocking parts of the camera lens.

It was with mattes that the first split-screen effects were pulled off. This is the traditional twin technique you probably associate with "The Parent Trap."

You shoot the scene twice, with the actor and a stand-in switching places, then combine the two strips of film into one. To disguise the seam, filmmakers make use of background elements in the shot, like a doorframe.

You can see that in "A Stolen Life," with two Bette Davises. Or here, where the actor played twins again in "Dead Ringer." In these movies, you can also see the use of the classic over-the-shoulder technique, where the actor speaks to a stand-in filmed from behind.

Split screens got complicated when one twin had to interact with another. Take this scene from "The Prisoner of Zenda," where Ronald Colman shakes hands with his identical cousin. The filmmakers put glass in front of the camera, part of which they covered in masking tape to matte out the head and shoulders of the actor's double. After filming the scene, they ran the film backwards and filmed it again with the actor on the other side, this time matting out everything but his head and shoulders.

That's a lot of work for a handshake shot that's only a few seconds long.

The split screen also usually required filming with a locked and fixed camera, resulting in shot compositions that could look very designed, with a sort of butterfly symmetry.

So, how did you get from that to a shot like this, from David Cronenberg's horror movie "Dead Ringers"?

In this film, not to be confused with the earlier Bette Davis movie "Dead Ringer," Jeremy Irons plays a disturbed pair of twin gynecologists. The movie was a big deal at the time because of how dynamic its shots were. In this scene, for example, you see the twins walk and talk together while followed by a fluid moving camera.

And a shot like this was only possible because of innovations from "Star Wars," which, in 1977, was the first film to extensively use motion-control cameras. This was groundbreaking for twin effects because directors could now program precise, repeatable camera movements to replicate the same shot over and over again. This helped visual effects artists film clean plates with no actors in them and use those plates to help merge people into the scene in postproduction.

Motion control became a mainstay of twin movies. And in 2002, it was among several techniques used to create the 130 twinning shots in the movie "Adaptation," where Nic Cage plays the identical Kaufman brothers.

One way the filmmakers made the effects invisible was with green-screen composites. That's when you film a twin on a green screen, isolate them, and comp them into a shot with the other twin, as seen here with the two Seth Rogen characters in "An American Pickle."

For this scene, Seth walked on a treadmill in front of a green screen so that when his two characters were comped together, they'd move at exactly the right pace. In "Adaptation," the green-screen method only worked for about 20% of the twin shots, mostly in the scenes that took place indoors.

Outdoors, green screens can create issues with green spill, when that green light ends up in places you don't want it. In these cases, the filmmakers on "Adaptation" turned to rotoscoping, which essentially means tracing by hand. With the rise of digital rotoscoping in the '90s, the technique became a major player in twin movies, allowing artists to comp together elements of different shots even if they weren't filmed in front of a green screen.

It's one thing to make two versions of an actor, but what about 80?

That's how many versions of Hugo Weaving appear in the "Burly Brawl" sequence from "The Matrix Reloaded." No amount of motion control, split screens, or rotoscoping could make a fight sequence with this many clones possible.

Instead, this scene took advantage of digital doubles. These CG humans were most often used for wild stunt sequences that no person could perform in real life. Because CG faces can look rubbery up close, digi-doubles are best used for wide shots, like those of the Agent Smith clones in "The Matrix Reloaded."

CG humans are also super expensive to create. The "Burly Brawl" scene alone cost Warner Bros. an estimated $40 million, a big chunk of the film's $150 million budget. So the digital-doubling method is best for a single sequence, not a workable option for doubling an actor throughout an entire movie.

Director David Fincher had to come up with a different solution for his film "The Social Network," where Armie Hammer played the Winklevoss twins.

Armie and his body double, Josh Pence, underwent a tailored training regimen to make their bodies as similar as possible. To transpose Armie's face onto Josh's body, the filmmakers settled on a facial-capture process very similar to the one used in video games like NBA 2K.

The VFX team first used a medical-grade laser to scan Josh's and Armie's heads for digital models. During filming, Josh wore tracking markers on his face so the VFX team could later object-track his facial movements. After, they recorded Armie inside a custom stage, which had computer-controlled lighting settings to match the light in every scene. In this stage, an array of cameras recorded every angle of Armie's face to provide what is called a face texture map, which could then be used to animate the CG model of his head, which, in turn, would get mapped onto Josh's body.

This basic process was also used to clone Paul Rudd for the Netflix series "Living with Yourself," except Paul preferred to act out his scenes alone, reacting to his prerecorded lines through an earpiece.

In scenes that required a stand-in, like this one, where Paul's character resuscitates his clone, the actor performed opposite a guy in a green suit, who VFX artists could replace later on.

The elaborate face-scanning approach wouldn't have been as feasible for "Us," which follows a family of four confronting their evil doppelgängers. The film built on all the innovations in twin effects over the past 100-plus years to bring this nightmare scenario to life.

With the advancement of face, head, and body replacements, technology could now be used in a Dr. Frankenstein kind of way to harvest different limbs and body parts, a similar method used to create the clones in many scenes from "Orphan Black."

From the start, "Us" required a lot of stunt doubles, including a photo double and a body double for each of the four main actors. One producer joked that there could be six versions of Winston Duke on set at a given time, all dressed in Howard sweatshirts and glasses.

Before shooting, Jordan and the VFX team would figure out which of the twins was guiding the action. They'd capture that first with the main actor playing the lead and their double playing opposite.

Then the actor and double would swap places. After shooting, the VFX team would patch the twin plates. In many cases, they'd decide to use a head from one plate and track it onto the body of the double in the other plate. But often it got more complicated, with artists piecing together by hand various parts of an actor's body from different shots.

Most modern twin movies and TV shows use motion-control cameras to smooth out this process, but in "Us," the script called for lots of handheld shots filmed with a more visceral camera style. Without motion control, the crew had to take careful notes of all camera motion in each scene, marking every position and tilt so they could replicate it after swapping the actor.

There were also scenes that the actors couldn't perform with a real double, like this face-off in the hall of mirrors, when the young version of Lupita Nyong'o's character gets choked by her evil doppelgänger.

The actor, Madison Curry, needed something to really grab onto, so they had her clutch a paper cup wrapped in green, which would be digitally replaced later on. A similar technique was used in "Enemy," where Jake Gyllenhaal acted opposite a tennis ball on a stick, its height representing his double's eyeline. This method can make the VFX team's job easier, because it means there isn't a whole body to erase later on, as seen here for "Orphan Black" and "An American Pickle."

None of these innovations happened in a vacuum. Even in 2019, "Us" relied on some of Hollywood's tried and true methods, like the good old split screen, for a number of shots. Every once in a while on set, Jordan Peele would say, "I'm thinking this shot is a Hayley Mills."

The dynamic twin scenes in his movie were a culmination of more than 12 decades of Hollywood ingenuity.

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