They heard the growls and shouting as they hurried down the corridor. Moving to the door where they heard the noises, they raised their shields and pushed the door open. The experienced teachers stopped in shock at what they saw. A troll was pushed against the ceiling, and Harry was ducking curses from behind some battered desks, and their fellow teacher, Professor Quirrell, who always struck them as harmless, was snarling as he cast curse after curse at Harry.