It’s enough to get actor Steve Zahn to beat his chest in frustration: the idea that audiences may not realize he wasn’t just monkeying around in a sound booth on War for the Planet of the Apes.

His character, an emotionally-fragile chimpanzee named Bad Ape, may be animated through CGI, but the programmers weren’t the ones squatting in the snows of British Columbia in tight unitards and cameras mounted on their heads, loping around on arm extensions until their thighs burned. That was all on the 49-year-old actor. The performance capture technology that allowed a human to undo five million years of evolution for the movie opening Friday still requires an actual performance.

“I read something on the Internets and someone said, ‘I can’t believe that Steve Zahn is the voice of Bad Ape,’” the actor recalled to RealClearLife, “And it struck me like, ‘Oh f—! I emailed (co-star) Andy Serkis that and he was like, ‘Yeah isn’t that crazy, it drives me nuts.’ That was just painful.”

Painful because Zahn threw himself completely into his first foray into performance capture technology, from watching a steady stream of YouTube videos of chimps for reference to constantly refining the character’s speedy, splayed gait. “All I did all day is be a chimp,” said Zahn. “When I couldn’t get out to the park, I’d go to the set, and I’d practice while they were shooting (other scenes).

“Then I’d go back to my little rented apartment in Vancouver with my arm (extensions) on, and I’m sure people who could see me from the 20th floor of the building next to mine were like, ‘What the f— is he doing?’ Every minute of the day that I was awake, I was thinking about it or doing it.”

But no one knows how little appreciation comes with the job than Serkis, who has played Caesar, the sandpaper-voiced leader of the apes in all three installments of The Planet of the Apes prequel trilogy. The British actor has consistently produced critically acclaimed performances since he first donned the Lycra to play Gollum in 2002’s The Lord of the Rings: The Two Towers. The problem is that it’s hard for Oscar voters to understand where the line is between the acting performance and the special effects.

“They are actually actors in a scene on the set with all the other actors in the scene doing the same job they’d be doing, whether they were wearing a three-piece suit or these funny Velcro pajamas that we make them wear,” said Weta Digital’s Dan Lemmon, the visual effects supervisor for War for the Planet of the Apes. “It’s just a different costume to put on, that’s all. It does get a little frustrating in terms of the lack of recognition.”

Andy Serkis has studied ape movements to play Caesar. (Weta Digital)

Lemmon, fresh off a visual effects Oscar win for The Jungle Book, has seen the technology burgeon over the past two decades—from the days when Serkis has to be filmed in a glorified toolshed for Lord of the Rings to being able to film in the mountains, “wading in snow up to our waists just trying to figure out where to place the cameras.”

“Whereas in Rise of the Planet of the Apes (2011), we shot mostly in the summer in ideal conditions in Vancouver, Dawn of the Planet of the Apes (2014) we shot in the forest with some rain,” said Lemmon.

“In War, we shot in pounding rain in the middle of the night, sub-freezing temperatures, in the snow in the side of the mountain … It was pretty crazy.”

But the overall concept has remained the same, whether it’s indoors or out. Those ugly gray bodysuits? They are there to hold dozens of balls covered in a reflective paint in place. The actors’ faces are also covered in white or green dots. All those markers are the points on the body that are picked up by dozens of special cameras lining an area called “the volume.”

The cameras feed the data of those markers’ movements into a computer program that plots out a three-dimensional “puppet” of the actor, explains Lemmon. With some help from the animators in a process called “re-targeting,” the Weta effects department can modify the puppet into a slightly different body shape—turning Zahn, for example, into the believable looking chimp. The same process is used for the actors’ facial expressions, picked up by those head-mounted cameras.

Even before cameras started rolling, performance capture veteran Terry Notary, who plays Caesar confidante Rocket in the movie, ran a simian boot camp to work on the realism his fellow actors’ ape movements.

It was a laborious process on the set, with each shot requiring four takes to make sure they get all the data that’s needed. A dozen performance capture support personal using an “array of computers, four rolling racks like rock and roll cases we use for what we call, ‘mission control,’” said Lemmon.

And it really did take an army to wage a war between the apes and Woody Harrelson’s human forces on screen. “At Weta Digital (in New Zealand) we had about 850 technicians and artists working on War for the Planet of the Ape,” said Lemmon.

There certainly has been a lot of technical evolution since the latex ape masks of the 1968 original Planet of the Apes.

“At least there’s a whole troupe of others dressed exactly like you,” Zahn said. “Trust me I’ve worn some crazy outfits over the years, so as an actor you’re prepared for all that.

“It’s kind of weird because you go through this whole process of simian training or ape training and you concentrate for weeks on it to try to get it to the point where it’s second nature, which is really difficult. And then once you’re with this troupe of others in gray unitards with backpacks and helmets with cameras on it, you just become this subspecies on the set.

“We would wander around base camp as apes going into the grip trucks and the dining tent, and people would ignore us because they were used to it.”

During filming, though, the actors’ hard work was not as easy to ignore.

“The animators can make you look like an ape,” Zahn said. “They can’t make you be one.”