Extracted from Harry Potter: The Creature Vault
Cornish pixies are mischievous, ill-behaved flying creatures that are relatively harmless but can cause damage if not restrained. They wreak havoc in Professor Lockhart’s classroom during his first Defence Against the Dark Arts class. The Cornish pixies make their second appearance in the Room of Requirement in Harry Potter and the Deathly Hallows – Part 2.
The Harry Potter books describe Cornish pixies as being blue, which the filmmakers faithfully represented. History has given us Cornish Blue roosters, Cornish Blue pottery, and an award-winning Cornish Blue cheese. But another possible provenance for the creatures in Harry Potter and the Chamber of Secrets is the historically based myth that pixies were a remnant of the Picts tribes, who lived in the Cornwall area during Celtic times and are said to have painted their skin blue.
For the films, a scale model of a Cornish pixie was created and painted an electric blue, and was then cyberscanned and animated by the digital artists. Depth of field was created by scattering the twenty or so pixies between the background, the foreground, and the middle at different heights in the filmed classroom. Actor Matthew Lewis (Neville Longbottom) had clips placed behind his ears to push them forward, to create the effect of two pixies pulling him up by the ears to suspend him above the room.