The relationship between machines and humans is much more productive behind the scenes of the new HBO show Westworld than it is in front of the camera. Using real-world performances and digital effects, the show’s creators have raised the bar on the long tradition of humans playing robots, building hybrid performances appropriate for a show about the rise of artificial intelligence.

Westworld takes place in a twisted theme park populated by incredibly lifelike androids and presided over by their morally compromised human creators. It can be hard to tell which characters fall into which categories until something breaks, which is where the computers come in. There are subtle tricks — twitches, stalls, inconsistent expressions — used to show what happens when robots perfectly designed to imitate humans malfunction and artifice can no longer obscure their nature. The success of this approach can be credited in part to the talented cast, but the show’s VFX supervisor Jay Worth explains that there was also a great deal of post-production work require to create the unnerving, unreal final product.

Worth, who has worked with executive producer J.J. Abrams’s Bad Robot Productions for the last decade, explained to Inverse that the scene in the first episode in which Old Bill, a first-generation robot at the park, drinks with Dr. Ford (Anthony Hopkins) wouldn’t have been possible without significant editing. Old Bill is rickety and moves like a looped Pirate of the Caribbean at Disneyland. While actor Michael Wincott has years of experience bringing characters to life, the VFX crew had to step in to help him give a believably “fake” performance.

“We changed his performance entirely, but it’s really subtle,” Worth says. “We gave him these little stopping and jerking things, his eyelids and hands and arms and how he moves. It was so effective in making it feel like this older model that was not quite as smooth.”

Old Bill on HBO's "Westworld" HBO

Cosa VFX, the company that handled the effects on Stranger Things and Agents of S.H.I.E.L.D., was behind the manipulation. Using the effects program Nuke, the team layered a lot of relatively simple effects to turn Bills larger gestures into chains of smaller movements.

“It’s all compositing,” Worth said. “You take certain portions of it, speed ramp and freeze it and do it all two dimensionally.”

Old Bill’s performance received the most computer assistance, but there several other characters in the first episode received the digital treatment. When Sheriff Pickett (Brian Howe) begins to short-circuit, half his face goes stiff. “We had a lot of fun with how his eyes worked, following the fly and malfunctioning,” Worth explained, noting that the show’s ubiquitous flies were often real and replaced digitally only when necessary. Similarly, Peter Abernathy (Louis Herthum), the android father of the pilot’s starring robot Dolores (Evan Rachel Wood) has a breakdown that Worth says require the post production team to do “really subtle things with his pupils and eyelids” that “made it feel like he was off, but not so mechanical.”

The approach the team took with Abernathy was different than the one they took with Old Bill because, on the show, the robots are not all functioning on the same code.

Still, Worth doesn’t want to take too much credit. He’s careful to consistently praise the actors, noting that much of the robotic activity was pure performance, and that his staff only helped make parts more convincing where needed.

“Everything that Abernathy does in his conversation with Dr. Ford, that’s all actor action,” Worth said. “We made him freeze every now and then. But the actors are really good at not blinking.”