Similarly, bones broken in non-magical accidents such as falls or fist fights can be mended by magic, but the consequences of curses or backfiring magic could be serious, permanent or life-threatening. This is the reason that Gilderoy Lockhart, victim of his own mangled Memory Charm, has permanent amnesia, why the poor Longbottoms remain permanently damaged by magical torture, and why Mad-Eye Moody had to resort to a wooden leg and a magical eye when the originals were irreparably damaged in a wizards' battle; Luna Lovegood's mother, Pandora, died when one of her own experimental spells went wrong, and Bill Weasley is irreversibly scarred after his meeting with Fenrir Greyback.

Traditionally, a witch or wizard's Pensieve, like their wand, is buried with them, as it is considered an intensely personal artefact; any thoughts or memories left inside the Pensieve are likewise interred with their owner, unless he or she has requested otherwise. The Hogwarts Pensieve, however, belongs not to any individual but to the school. It has been used by a long line of headmasters and headmistresses, who have also left behind their life experience in the form of memories. This forms an invaluable library of reference for the headmaster or headmistress of the day.

When I dreamed up Errol, the aged, long-suffering and overworked Weasley family owl, I had in mind a picture I thought I had seen, which featured a very comical, large, fluffy, grey, bewildered-looking bird whose breed I had never known. In fact, I wondered whether it had been a real photograph, or whether imagination was distorting the image. It was with sheer delight, therefore, that I rounded a corner on my first ever visit to the aviary at Leavesden Studios, where they were filming Harry Potter and the Philosopher's Stone, and saw a line of big, grey, fluffy, bewildered-looking owls blinking back at me, each an exact replica of the half-remembered picture I thought I might have dreamed. They were all playing Errol, and they are Great Greys.