They’re amongst the most terrifying monsters in the films – so they needed to scare the audience.

Dumbledore casts fire spell against the attacking Inferi in Horcrux Cave.
© JKR/Pottermore Ltd. ™ Warner Bros.

Extracted from Harry Potter the Creature Vault.

The filmmakers didn’t want the bewitched Inferi to be stereotyped as just another film monster – ultimately they were designed to elicit not just fear, but also sympathy.

Full-sized models of the creatures were sculpted for scanning, as the Inferi were destined to be completely computer-generated creations. The cyberscans of the models were painted in the computer, and texture was added to give them the right amount of ‘fleshiness’. As the same time, a digital ‘skeleton’ was implanted in them so they could be animated.

To determine how the Inferi would move, director David Yates had a group of men and women dancers assembled to enact the Inferi emerging from the water and grabbing at Harry.

These choreographed sequences were filmed with motion-capture technology, and the resulting footage was combined with computer animation to create the final performance. This technique made the Inferis’ movements less artificial and more human.

‘Not having them groan or stick their arms out helped get them away from anything zombielike,’ explains visual effects supervisor Tim Alexander. ‘We wanted them to move more gracefully when coming out of water.’

The Inferi are seen both on land and underwater, which was a challenging divide for the visual effects department to bridge, especially with the flickering firelight that illuminates the scene.

‘The underwater world was difficult because of their sheer number, and the interactive light from the fire,’ says Alexander. The animators ultimately developed new VFX techniques from video game technology.

Harry Potter: The Creature Vault book cover