Percy Weasley, being the Prefect he is, was in his dorm, working on his writing, being very concentrated. He had to deliver it to Snape much earlier than he had asked Percy to, Percy wanted to show him that he could do things much better than other students.

Percy was writing when he heard a lot of noises outside, so he got up, opened the window and shouted.

"Hey! Stop all the noises, I'm trying to concentrate!"