No one could wait for the holidays to start. While the Slytherin common room and the Great Hall had roaring fires, the drafty corridors had become icy and a bitter wind rattled the windows in the classrooms. Worst of all were Professor Snape's classes down in the dungeons, where their breath rose in a mist before them and they kept as close as possible to their hot cauldrons. Snape had come to the common room one day and taught them all warming charms until most of them could cast it nonverbally.