Marauder's Map

The Marauder's Map is a magical item which features in the Harry Potter series of novels by J. K. Rowling. Created by Moony, Padfoot, Prongs[?] and Wormtail, the map on first appearance is a piece of blank parchment, but when the user says "I solemnly swear that I am up to no good" the map appears, showing Hogwarts, and the location of everyone within the grounds. The map also gives information on how to open the secret passageways.

The map was given to Harry by Fred and George Weasley, who found it while unattended in Filch's[?] office. The map made its first appearance in Harry Potter and the Prisoner of Azkaban

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In Harry Potter and the Prisoner of Azkaban, Snape finds the map in Harry's possession, and tries to force it to reveal its secrets; the map responds by insulting him. Snape suspects dark magic at work, though given that the map's creators, James Potter[?], Sirius Black, Remus Lupin and Peter Pettigrew, detested Snape, they may have added these insults specifically for him.