" [A witch] might even – and this will make you jump – she might even be your lovely school-teacher who is reading these words to you at this very moment. Look carefully at that teacher. Perhaps she is smiling to you at the absurdity of such a suggestion. Don't let that put you off. It could be part of her cleverness.

I am not, of course, telling you for one second that your teacher actually is a witch. All I am saying is that she might be one. It is most unlikely. But -- and here comes the big "but" -- it is not impossible. "

― Roald Dahl