Remus Lupin had been bitten by a werewolf as a child, and the lycanthrophy was taking effect when the full moon was out. He transformed into a werewolf and approahced Harry Potter, but was blocked by Snape. As he was about to attack, he was tackled by Sirius Black, who had turned into a dog.The two fought with each other and Sirius ran away, chased by Remus. Catching him, he threw him away but Harry Potter hit him with a rock. The werewolf roared at Harry and ran to him but heard another werewolf calling and decided to follow the sound and left.