* "Patronus: An anti-dementor, a guardian that acts as a shield between you and a dementor. A positive force, a projection of the very things that a dementor feeds upon - hope, happiness, the desire to survive - but it cannot feel despair as real humans can, so the dementors can't hurt it. Each patronus is unique to the wizard who conjures it. To conjure a patronus you have to concentrate with all your might, on a single very happy memory"
-- J.K. Rowling, Harry Potter and the Prisoner of Azkaban, page 237--