Goodness, that's quite the postscript :). Have you been flamed for a story before?
This was utterly delicious, and the idea of Percy and the twins is lkdsjf.
Percy couldn't understand how the ghostly Professor Binns could give this lecture to every year level, at least twice during every school year, and still need to consult his notes, but there was no denying the obvious dependence on them.
You know, I wonder if it's possible for a ghost to learn? They're presumably static, so there's no way to form new neural pathways, so if Binns needed to refer to his notes before he died, it makes sense that he'd still need to as a ghost.