While "Star Wars: The Force Awakens" enters the Academy's VFX bake-off on Saturday as the obvious frontrunner, everyone wants to know how ILM did the harrowing bear attack in "The Revenant." Here's a behind the scenes glimpse from VFX production supervisor Richard McBride.

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The Revenant

"What was interesting, thinking back to the early discussions with [director] Alejandro [González Iñárritu]," recalled McBride, "was how it was all about movement and planning and choreography, but always coming back to how an actual bear attack would unfold. And the other thing was getting into the mindset that this was not a monster: it's in its natural habitat and just behaving as a normal animal would [a mother protecting her cubs]. Alejandro wanted the attack to be sudden and wanted us to feel close to the action and immersed in every detail," added McBride, who was joined by animation supervisor Matt Shumway.

However, unlike the opening Native American ambush, the grizzly bear mauling was conceived as "one continuous take" in a primordial-looking rain forest. That is, it was seamlessly stitched together with even greater skill than "Birdman." Overall, it was a brilliant collaboration between Iñárritu, cinematographer Emmanuel (Chivo) Lubezki, Leonardo DiCaprio, production designer Jack Fisk, the stunt team, ILM, the sound editing/design team of Martin Hernandez, Randy Thom and Lon Bender, editor Stephen Mirrione and Technicolor in post.

The ILM bear team first met with "Mark of the Grizzly" author Scott McMillion and learned about all of the potential scenarios that can happen in the woods. It was based on chance encounters, such as a bear protecting its cubs, which was the basis of attack in "The Revenant."

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The Revenant

A crucial reference, though, was online footage of an actual bear attack at a German zoo, in which a man drunkenly stumbled into the cage. What was most remarkable was the seeming randomness of the attack and that it was shot without cuts. This formed the basis of the choreography. "Initially, a stunt team worked out the choreography of how they were going to tug and pull the actor during the mauling," continued McBride. They shot the scene on location in freezing cold and rain and staged the beats of the attack.

"For us, the VFX team, we wanted to keep Leo visible and also keep it kind of messy, so once we had the camera work there, we positioned our stuntman in a way that he was grabbing and pulling in all the right places where we thought the bites were gonna be. And keeping him at a distance where there would be a little less paint work in getting him in and out of the scene and having our bear on top of him. Ultimately, the paint work was extensive because of how close we were to the action."

The most interesting part of the attack was the quiet or stillness that occurred in between the vicious moments. The anticipation of what was going to happen next made it scarier."When Leo got involved, he added a whole other beat where you're getting more sympathy for the bear," McBride continued.

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The Revenant

In terms of the animation, ILM took advantage of its recent fur work on the upcoming "Warcraft," but needed to up its game considerably. "One of the unique aspects was there wasn't the customary separation between grooming and simulation," McBride emphasized. "This project pushed the pipeline so that it adhered to the initial look that you built into it. So there was the simulation of flesh over the bones and then a layer of skin that got another [round] of simulation and then the fur got simulated on top of that. This provided complexity to the motion. But we had to dial it back because if you looked at the reference, sometimes the shimmer on the fur looked too computer-generated the way it was blinking on and off."

ILM used its Zeno pipeline for simulation, Maya for animation and Pixar's RenderMan for rendering. Meanwhile, the modeling team built shapes and controls that provided a very naturalistic performance for the grizzly.

Other considerations included how wet the fur was going to be, how it was going to react to the light and how we were going to see the wound and the redness of the blood.

The Revenant

"These nuanced tics and gestures and articulation in areas of the face, eyes, snout and mouth avoided the look of menace," McBride said. 

"There's a moment where the gunshot has already happened and they're both damaged: the bear is bleeding and Leo's torn up. And the camera goes back to the bear and she's torn: the cubs are on one side and this threat is on the other and she's struggling to stand. She could walk away but goes for one last lunge in her dying moment to protect her cubs," McBride concluded.

No wonder the bear attack has garnered so much industry buzz—it's the dramatic essence of great VFX.