The clatter made Septima's heart jump into her mouth with fear, half blinded and frightened of the unknown. But Parvati's squeak of shocked recognition reached her before she could do anything foolish like hex a student, thinking she was... something more unpleasant.
Blinking, Septima didn't lower her wand. "You do know that students are meant to be in their common rooms," she said angrily, and was embarrassed by the way her voice and wand hand were both quavering slightly with reaction.