In addition, the Patronus spells usually take the shape of an animal, but in this case the charm arrives as a sort of compact, spherical comet. A large box covered in LEDs was used on set to provide some interactive light and help with cast eye lines and Double Negative generated the Patronus as a pulsing ball of energy built around the practical lighting effect. The team referenced bioluminescent deep sea creatures for an ethereal effect, using a combination of Houdini and proprietary packages, dnSquirt and DNB.

For the Horcrux, Rising Sun Pictures (under the supervision of Sean Mathiesen) devised a contorted, tortured effigy/soul of Voldemort in the middle of some kind of seizure. Yates and Burke both responded well to the design, but requested that it should be 20 to 30-feet tall to be more menacing. They explored all kinds of meat, cloth, smoke, organs, ink and slime during pre-production. In the end, it was constructed of the slime and scum and detritus from the pond where the scene plays out in the film.

The Dementors were designed to be made of smoke instead of appearing merely shrouded in smoke. They used matchmoves, published geometry and digital doubles created in-house and brought them into Cinema 4D, played with ideas of separating smoke and building it from the ground and then merged them with cloth and robes and exported them out using FBX. The Maya cloth team took over and worked with the Houdini team and it was composited in Nuke.

Meanwhile, Cinesite (under the supervision of Holger Voss) used its proprietary csSkinShader for subsurface work on Voldermort's nose, generating textures from photographs shot using cross-polarized and non-polarized lights and lenses to extract highly detailed pore maps; csFluidShader to render Maya Fluids with RenderMan for the volumetric Patronus Doe effect in helping Harry find the Sword of Gryffindor; and csPhotoMesh to reconstruct terrain information from photographs for the establishing shot in the Windswept Hill sequence.

"It works well being split up because they're quite different movies," Burke offers. "Part 1 is very dense and sets up Part 2 brilliantly, which is more of an action movie."

Bill Desowitz is senior editor of AWN & VFXWorld.