Meanwhile Professor Binns, the ghost who taught History of Magic, had them writing weekly essays on the goblin rebellions of the eighteenth century. Professor Snape was forcing them to research antidotes. They took this one seriously, as he had hinted that he might be poisoning one of them before Christmas to see if their antidote worked. Professor Flitwick had asked them to read three extra books in preparation for their lesson on Summoning Charms.