Animation supervisor Michael Eames recalls, “As well as the enormous technical challenges, here we had a creature with more to it than simple, animalistic behavior. It was necessary to bring some character to Buckbeak.” Eames and his team studied both birds of prey and horses — on film and during visits to zoos. Cuarón had a clear idea of both what Buckbeak was like — coltish, a little dangerous, a bit of a wild adolescent — and of the nature of his relationship with Harry — The Black Stallion was cited as a reference. Though accepting of Harry, it’s an animalistic acceptance, based on mutual respect. The film did not allow for a leisurely exposition of the boy/bird friendship. “There are real difficulties with creating character in a creature such as this, in the limited scenes you have available,” adds Eames. “It has to live in the space — to be ‘real’. It doesn’t talk and it has a beak — with all the lack of expression implicit in that. So you look for everything that can help you convey what you want. We used cues from the actors — interaction points. For example, when Harry and Buckbeak first meet, we used a slight slip in Harry’s posture, bouncing it off Buckbeak as a reaction.”

Whomping Willow
Initially developed by MPC for Harry Potter and the Chamber of Secrets, the Whomping Willow returns as a more gnarled and twisted version, now located in the wild countryside beyond the walls of Hogwarts. Accurate previs data was used by both the physical effects team and the visual effects crew to plan for sequences where Hermione and Harry are swung around by the tree, and in another where Ron is dragged along the ground by the Grim. The physical effects team engineered Hermione onto a rig, which swung her around, and the digital team tracked her motion and built the swinging branches around her. Fully digital versions of the children or parts of their bodies were used for shots that would have been impossible to shoot in the studio. For both the Whomping Willow and the Grim drag sequences, MPC visual effects supervisor Paddy Eason filmed in studio before bluescreen. The studio was of a limited size, so the team, led by CG supervisors Simon Clutterbuck and Peter Muyzers, built a digital landscape. They extended the set out to the horizon, mirroring the real exterior shots with elements, including rocks, ferns, heather, a lake, forests of pine trees, mountains and the sky. Because of Cuarón's highly mobile camera technique, the environment needed to be in 3D rather than a traditional matte painting. The digital landscapes were also used elsewhere in the film — during flashback shots and in three establishing scenes, where the Whomping Willow and Hogwarts’ exterior are seen in spring, summer and fall.

MPC oversaw the transformation of Professor Remus Lupin (above left, played by David Thewlis) into the Werewolf.

MPC’s other work includes the metamorphosis of Peter Pettigrew to alter ego “Scabbers” the rat and back again, and the transformation of Professor Remus Lupin into the Werewolf. They created the invisibility cloaks, a digital matte painting of Hogsmeade village, a photoreal bird, wand effects, digital snow enhancement and many other effects for the movie. The team also developed the film’s characteristic title sequence, encompassing live-action plates composited together with miniature 3D models and a 3D animated flying Harry Potter logo.

Dementors
The big challenge for ILM was the character of the Dementors. Some tests had been done using a puppet under water and Cuarón really liked the look, so production asked ILM if they could use the current technology of cloth simulation to mimic the tests. Most cloth simulation software is meant to simulate how cloth normally moves in gravity. Because the tests were shot under water, however, they had a slow motion feel, much slower than normal. It was necessary for the team to adjust the timing of the cloth movement. It was supposed to be spectral, so the team turned the gravity way down. The material floated, like seaweed. They used digital wind sources and other techniques to move the fabric around and get it to go in the desired direction. “The tendrils were such an important character piece we really had to do whatever it took to get them where we wanted them,” shares George. David Andrews was the animation director. It was very hard for him to animate a character that has no face, no eyes, just body movement. The Demetor was only fabric over a skeleton armature. The initial tendency was to give the creatures frenetic actions. “Alfonso’s direction was, no, these guys know they’re going to get you and they’re not in any hurry. They move like royalty. They go very slow. They’re a force that you cannot stop,” says George.

ILM also developed the Boggart, the creature that changed into what frightens you. The most challenging aspect was the design work. For characters such as the Boggart there was no direct path from the design to making it happen. It was experimentation, trying other things. The director didn’t want it to be solid, but he also didn’t want it to be a spirit. It took a long time to get the director’s vision.