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 Grimmauld Place. Hermione takes Phineas from Grimmauld Place during "Harry Potter and the Deathly Hallows" and uses Phineas to obtain information about events at Hogwarts. Dumbledore also uses two other former headmasters in a similar fashion when Arthur Weasley is attacked by Nagini in the Ministry of Magic. A portrait is also seen carrying messages between the Minister for Magic and the Muggle Prime Minister in the opening of "Harry Potter and the Half-Blood Prince". Another form of closed communication used in the books and movies is a set of mirrors which belonged to Sirius Black. Sirius gives Harry one