The most boring class to the Slytherins, even Hermione who enjoyed learning in general, was History of Magic, which was the only class taught by a ghost. Professor Binns had been very old when he had fallen asleep in front of the staff room fire and got up the next morning to teach, leaving his body behind him. The Slytherins used his class to do homework or read up on their favourite class, whereas the Gryffindors, who they shared the class with, usually mucked around loudly or slept.