Layla jumped when a boy swore. A teacher was passing at that exact moment - unluckily - and she deducted 10 points from Gryffindor. Layla didn't really understand the point system yet, but she knew enough to realise that the subtraction was bad, so she glared at the fellow 11 year old.
The next day
Defence against the dark arts did not seem fun to Layla. In fact, it sounded like something that could go horribly wrong. She had read A History of Hogwarts, and that explained the basics of dark arts without even trying! The map she was given was useless. The general message was that the classroom was in the dungeons, but where exactly in the dungeon area?
Layla stumbled into a random room in the dungeons. Taking a moment to look at her surroundings, she heard the door slam behind her with a loud CRASH! "No! Open the door!" She ran over to try the door handle, but it had mysteriously vanished. Well, duh, this was a magic school! A mad cackling drifted in through the cracks in the door. "Help!" She cried, but doubt overwhelmed her and she thought no-one would find her.