Buckbeak and Trelawney are introduced for their importance later in the book (and series). The third-years Defense Against the Dark Arts class is a change as Lupin has them getting practical experience with Neville getting a chance to shine for the first time. Sirius Black's infiltration of Hogwarts on Halloween as well as Crookshanks antics make things lively. The Dementors and the Grim reappear, unfortunately for Harry during Quiddich resulting in losing both the game and his broom. The introduction of the Marauder's Map and Harry sneaking off to Hogsmeade to overhear information about Sirius Black (This one chapter of the book is one place in which the film adaptation is superior to Rowlings' writing).