Good, so now everyone, not just the Gryffindor captain yes he had heard her knew who had died in this room. "We're looking for Professor Binns' outline vhen, class."

He paused and gave them a look, then gestured toward Knox's chair. "Please form a line and vhen one at a time, you may test vhe spell by vhinking of Binns and looking for his shadow. Again, only you vill see it vhen you yourself test vhe spell." And he gestured for them to go forth and practise it on the chair near the fireplace. The only other occupied chair in the room, in other words.

Class was winding down anyway. He'd find it amusing if Knox glowed green because of where she was sitting.