Professor Binns is absent from the Harry Potter movies but in the books he’s a ghost who teaches Magical History in Hogwarts. First of all, ghosts in general makes me wonder about life and eternity. Ghosts in Hogwarts are trapped to repeat the same monotony of their unlife, presumably until the inevitable heat death of the universe, without any rest ever. But existential questions aside, why does Hogwarts let a ghost teach? Wouldn’t that take away the job from someone who actually needs it? Because ghosts don’t need anything. They don’t need food, they don’t need sleep, they don’t even really need material possessions considering they’re unable to touch anything physical. If Binns is allowed to teach at Hogwarts wouldn't it be cheaper to “hire” an entirely ghost staff? In addition to the house elves who don’t get payment either, of course. In fact, is the only reason Binns is allowed to teach the fact that it’s so cheap, considering that his only real character traits are that he can’t concentrate on his students and instead only repeats the same curriculum, which in turn no student can concentrate on because it’s so boring. The books repeatedly mention that Binns doesn’t even remember the names of any of his students, and that the only one who actually learns anything about Magical History is Hermione. It seems counter productive to have a teacher who is obviously unable to actually make children learn. So many unanswered questions.