Cameron explained in the interview why such a complex rig was required, understanding that the infinite nuances of the human face would not be captured any other way. Subtle eye movements, he felt, were key. 

“It’s the eyes, and it was also the entire face. We have almost as many muscles in just our face as we have in the entire rest of our body. So the systems previously that we used were good at capturing body performance, we basically did the same thing. But we completely changed the way the face was captured. The way Zoe’s mind reacts with her facial muscles is going to be very different than the way Sam’s does and the other actors do. So it wasn’t just a question of the perfect CG model for these characters.

Meanwhile, Saldaña felt that such attention to detail was a wonderful way of unlocking the spirituality of the characters; The Na’vi are connected to their planet — in some cases quite literally (they have psychic tendrils that lace into living creatures). The tech, she feels, was secondary to the trust created between actors and a director who were free to be themselves.

“Everything comes into consideration, from their physical anatomy to the slightest detail, obviously with Jim guiding us. But then there’s the spiritual side of the characters. The Na’vi don’t have a word for ‘lie.’ They don’t live a lie; they don’t know what a lie is. Everything they do is so genuine and pure, even from the way they turn to address each other, has a trust in it. We would always talk about that.

But that trust was achieved through throbbing temples. Early renditions of the facial rigs, it turns out, didn’t fit quite well.