'Weta Digital's senior visual effects supervisor Joe Letteri explains, "The motion capture we did with Kong was a new way of using technology. It's a combination of things that have been done in the past, but we've brought them together in a unique way. We have created a system that's based on emotional states. It depends on us figuring out all the muscles of the face and understanding the correspondence between a human facial system and a gorilla facial system. What that allows us to do is to look at how muscles work together to create believable expressions. We then extract this muscle-by-muscle technique into something that's much more emotional. The facial animation system for Kong is the next generation of the facial system we built for Gollum." ...
'Once principal photography began, Andy Serkis was called to be Kong for his fellow actors, providing on-set reference and functioning as an emotionally present participant in the scenes. During these instances, the actor performed in a custom-made Kong suit - fitted with musculature, arm extensions and a hood that extended the shoulders and created a no-neck look - that allowed Serkis to mimic the physicality of a gorilla, such as walking on all fours. To supply Kong's roaring, the sound department developed a "Kongalizer," a system that took Serkis' wordless vocal responses (picked up by a headset mic), ran them through a computer (which dropped the range and increased the size), and then broadcast them through a wall of speakers in real time. For key, intimate moments with Watts, the suited and Kongalized Serkis not only partnered in the scene, but also provided sight lines for the actress, often from the correct vantage point of 25 feet off the ground - accomplished by raising the actor in a cherry picker.
'Peter Jackson elaborates, "Andy was able to be on-set every day, and he was able to stand in for Kong. He's obviously not 25 feet tall, but we were able to put him on ladders, up in cherry pickers, do whatever we needed to do to make him the right height. Most critically he was there for Naomi, who would be delivering this incredible performance as Ann relating to Kong…and she had Andy to look at and talk to. She had Andy's eyes to look into when she wanted to make these moments as real as possible. I think it would be virtually impossible for an actor to get that level of performance if they were just acting to a yellow tennis ball on a stick. It just would never happen that way. So it was critical to have somebody there."
'Serkis adds, "You know, these were absolutely significant moment-to-moment emotions that were traded between us. And so really, I could have been wearing anything. It was very much through the eyes, but once we locked into each other…that was it. You have to give as truthful a performance as in any other kind of film. I mean, Pete makes fantasy films, but he does it through a dramatic keyhole so that there is a sense of total reality."
'Watts comments, "I had no idea what to expect. I had been told that a good two-thirds of the movie was opposite Kong, so how would that translate into the performance? I thought, 'Okay, I'm going to be looking at a mark on a stick and pretending there's a connection…ooh, this is going to be hard.' But with Andy doing it, I had a pair of eyes to look into, a soul to connect with - what a relief! And what a privilege. I could not have done anything without him. I don't know that there's another actor out there who could have done what he did with the amount of preparation and work he put into it. It was mind-blowing on a daily basis."