Harry prepares to play in his first Quidditch match by reading a book about the game. Professor Snape spots him reading it outside the school castle and confiscates it, claiming that library books can't be taken outside. As Snape leaves, Harry and Ron notice that Snape is limping. Later, when looking for Snape in the staffroom to ask for the book back, they see Filch bandaging Snape's bloodied leg while Snape is asking, "How are you supposed to keep your eyes on all three heads at once?" Snape sees Harry watching him, and responds with fury. Harry assumes that Snape tried to get past the three-headed dog at Halloween, and probably let the troll into the castle to create a diversion.
During the Quidditch match, Harry's broom starts to behave strangely, as though Harry cannot keep control of it. In the stands below all the aerial action, Hermione notices Snape looking at Harry and muttering. She assumes that Snape is jinxing the broom. Hermione sneaks under the bleachers where Snape is sitting and uses her wand to ignite the hem of his robes. As soon as Snape notices that he is on fire, Hermione takes the flames back, into a small jar, so that Snape will never know what happened. While Snape is distracted, however, Harry is able to regain control of his broom. He catches the Golden Snitch-the winged ball whose capture means the immediate end of the game. In Hagrid's hut after the match, Hagrid dismisses the idea that Snape was interfering with Harry's flying, and reacts with shock when he learns that the three children know about "Fluffy"-what he calls the three-headed dog. He urges them to meddle no more in this "top secret" matter, which involves the dog, what it guards, Dumbledore, and someone named Nicolas Flamel.
Nicolas Flamel, whom Hagrid inadvertently mentions at the end of this chapter, was a real person, a fourteenth-century French bookseller, clerk, and-most significantly for readers' purposes-alchemist. Alchemy was the medieval "science" devoted to making gold from other metals. Tradition (begun by Flamel himself) states that Flamel used instructions from a Hebrew book, The Book of Abraham the Jew (the existence of which Flamel claimed was revealed to him by an angel in a dream), to develop either a powder sometimes referred to as "philosophical tincture," or a physical object called "the philosopher's stone." Not only was it supposed to initiate the transformation of baser metals into gold, it was also believed to be a distillation of the essence of life itself-a belief that led to rumors of Flamel's immortality long after his death in 1418. In fact, according to U.S. News & World Report, people rummaged through Flamel's house as late as 1816 in search of his secrets (Vicky Hallett, "Alchemist's secret," U.S. News & World Report, 26 August 2002). Rowling's first Harry Potter novel was originally published in Britain as Harry Potter and the Philosopher's Stone. Because of concerns that American readers would not understand the reference to Flamel and alchemy, however, the book reached U.S. shelves with a reference to the "sorcerer's stone," despite Flamel's continued presence as a character in the novel.