Helena was unsettled.

A feeling she hadn't been able to shake off after the meeting in Headmistress Truebridge's office. Something was going on unseen in the castle and she was sure of it given all the previous events and incidents during the year so far. Call it instinct if you will or gut feeling but it was that feeling that drove the Grey Lady to float into the corridor outside the Ravenclaw Common Room.

Floating up soundlessly to the Bronze Knocker the elegant lady ghost started to investigate around the knocker. Had it been affected by the small earthquake that had caused a passage to be revealed behind her mother's statue?