While the doubles/clones thing has been done quite well recently—Orphan Black, Netflix's What Happened To Monday?—that doesn't make it any less of a visual and logistical challenge for the crew.
"That was a big learning experience for all of us—how to stage those scenes, which tools do you use?" Montpellier says. "We wanted to create a seamlessly staged scene with two characters walking around each other and having natural conversation."
Doing that means placing as few restrictions on Simmons as possible so his performance, and not some technical tricks, distinguish the two Howards. Achieving that goal does require plenty of technology in practice, however.
"We ended up using a motion-control camera rig that could repeat shots to the exact frame accuracy," Montpellier says. "A lot of times, we'd approach these scenes with JK as Howard 1 and a stand-in so he could perform against someone on the other side of the frame. You'd move around the room [and] we'd follow him with the techno-dolly, this huge motion-control rig with a computerized robotic arm that can repeat the shot.
So we'd perform one side of the shot, then JK would go get changed. During that time, we'd edit his audio and put all of that together. When he'd show up a half hour later as the other Howard Silk, we'd repeat the camera move, they'd repeat the blocking, and the stand-in would take the other side. We'd repeat the shots, but it might take numerous takes because the timing might be slightly off. And before we'd leave that setup for the next scene, our VFX team is there recording everything and making rough composites on set so we could see that everything was lining up properly before breaking down. You might end up with 10 crewmembers staring at a lamp in the frame because it's a double exposure. 'Oh, is it good, or is it off?' It was very much a learning experience."