Harry Potter and the Prisoner of Azkaban attacked by a big black dog, which Harry has seen several times before. The dog drags Ron through a tunnel under the Whomping Willow into the Shrieking Shack. Harry and Hermione follow, and there is a brief standoff when they find Ron with Sirius Black, who has transformed from the dog. Lupin enters, and they explain the situation to Harry and his friends: Lupin is a werewolf, which led to his friends James Potter, Sirius Black, and Peter Pettigrew becoming animagi. Lupin explains that Scabbers is Pettigrew in his animal form; he has been hiding from Black, whom he had
Fictional universe of Harry Potter and put his/her head into the flames, causing it to appear in the fireplace of the wizard with whom he/she intends to speak. This use of the Network is first seen in "Harry Potter and the Goblet of Fire" when Harry sees Amos Diggory's head in the Weasleys' fireplace at The Burrow, talking to Molly Weasley. Harry also uses this method to communicate with Sirius Black on several occasions during the series. The etiquette surrounding using the fireplace for communication is not explicitly addressed in the series. Dumbledore tells Harry it is not polite for a wizard to apparate (appear