Remus Lupin

As the night of the full moon approached, the night when Remus would transform into a werewolf, he and Sirius argued.
Sirius frowned. He pointed his finger at Remus and said peremptorily:

• I'll go with you today.
  Remus shook his head, looking at Sirius reproachfully.
• It's too dangerous. I could hurt you.
  Sirius just rolled his eyes at this, but stopped arguing.
  When the full moon arrived, Remus went through the Willow to the Howling Shack, and Sirius crept behind him in the form of a black dog. The moon appeared outside the window. It was time for the transformation. Remus transformed into a werewolf and spotted Sirius hiding behind the sofa. He attacked him, scratching his side. Sirius was unable to dodge and whined in pain. The claws sank deep into his skin. Remus nearly tore Sirius to pieces, but he miraculously survived. Later that night, he returned to human form again, terribly exhausted from the transformation. He noticed that Sirius was literally bleeding out. He had lost consciousness and was now lying in human form in a pool of his own blood. Remus picked him up and carried him to the infirmary. There, Madam Pomfrey attended to them both.