Question: what is the difference between a ghost and an inferi?
Answer: "The Inferius is a corpse that has be reanimated by a Dark wizard's spells. It is not alive, it is merely used like a puppet to do the wizard's bidding. A ghost, as I trust that you are all aware by now, is the imprint of a departed soul left upon the earth ... and of course, as Potter so wisely tells us, transparent."