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".