<P> Likewise, it is not possible to make oneself immortal unless one makes use of an object of great power to sustain life, such as the Philosopher's Stone or horcruxes . If one were to possess the three Deathly Hallows, it is fabled that they would possess the tools to become the "master of death". However, it is hinted that to be a true "master of death" is to be willing to accept that death is inevitable . Other methods of extending life include drinking unicorn blood, which will keep a person alive even if death is imminent, but at the terrible price of being cursed forever . Being magical can contribute to one's longevity, as there are several characters in the series who are unusually long - lived (such as Griselda Marchbanks, who was an invigilator during Albus Dumbledore's O.W.L examinations). It is revealed by Nearly Headless Nick in the fifth book that all witches and wizards have the choice of becoming ghosts upon dying; however, it is described as "a pale imitation of life". Snape states that a ghost is merely "the imprint of a departed soul left upon the earth". </P> <P> Death is studied at the Department of Mysteries in a chamber containing an enigmatic veil, which Rowling has described as "the divide between life and death". With regard to what is on the other side, she elaborated: "Do I believe you go on? Yes, I do believe you go on . I do believe in an afterlife, although I'm absolutely doubt - ridden and always have been but there you are ." Sirius falls through this veil in Order of the Phoenix after he is hit with a curse from Bellatrix . </P> <P> The Principal Exceptions to Gamp's Law of Elemental Transfiguration is a magical theory mentioned by Hermione and later repeated by Ron in the final book . She explains that food is one of these: witches or wizards can cook and prepare food using magic, and even multiply it, but not create it out of nothing . There are numerous examples in the series of food appearing to have been conjured from nothing, such as the sudden materialisation of ingredients in the pots of Molly Weasley's kitchen and when Professor McGonagall creates a self - refilling plate of sandwiches for Harry and Ron in Chamber of Secrets . In all cases, these events can be reasonably explained as food either being multiplied or transported from elsewhere . One example of the latter is banqueting at Hogwarts--the food is prepared by elves in the kitchens and laid onto four replica tables, directly below the actual house tables in the Great Hall . The food is then magically transported to the tables . </P> <P> This is the only exception mentioned explicitly in the series . However, Rowling herself has stated once in an interview that money is something wizards cannot simply materialise out of thin air, or the economic system of the wizarding world would then be gravely flawed and disrupted . While the Philosopher's Stone does permit alchemy, this is portrayed as an extremely rare, even unique, object, whose owner does not exploit its powers . </P>

Which of the following never taught harry defence against the dark arts