The whole class looked around at Harry, who hastily tried to recall what Dumbledore had told him the night that they had gone to visit Slughorn.
“Er—well—ghosts are transparent—” he said.
“Oh, very good,” interrupted Snape, his lip curling. “Yes, it is easy to see that nearly six years of magical education have not been wasted on you, Potter. Ghosts are transparent.”
Pansy Parkinson let out a high-pitched giggle. Several other people were smirking. Harry took a deep breath and continued calmly, though his insides were boiling, “Yeah, ghosts are transparent, but Inferi are dead bodies, aren’t they? So they’d be solid—”
“A five-year-old could have told us as much,” sneered Snape. “The Inferius is a corpse that has been 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.”
“Well, what Harry said is the most useful if we’re trying to tell them apart!” said Ron. “When we come face-to-face with one down a dark alley, we’re going to be having a look to see if it’s solid, aren’t we, we’re not going to be asking, ‘Excuse me, are you the imprint of a departed soul?’”
There was a ripple of laughter, instantly quelled by the look Snape gave the class.
“Another ten points from Gryffindor,” said Snape. “I would expect nothing more sophisticated from you, Ronald Weasley, the boy so solid he cannot Apparate half an inch across a room.”
“No!” whispered Hermione, grabbing Harry’s arm as he opened his mouth furiously. “There’s no point, you’ll just end up in detention again, leave it!”
“Now open your books to page two hundred and thirteen,” said Snape, smirking a little, “and read the first two paragraphs on the Cruciatus Curse.”
Ron was very subdued all through the class. When the bell sounded at the end of the lesson, Lavender caught up with Ron and Harry (Hermione mysteriously melted out of sight as she approached) and abused Snape hotly for his jibe about Ron’s Apparition, but this seemed to merely irritate Ron, and he shook her off by making a detour into the boys’ bathroom with Harry.
“Snape’s right, though, isn’t he?” said Ron, after staring into a cracked mirror for a minute or two. “I dunno whether it’s worth me taking the test. I just can’t get the hang of Apparition.”
“You might as well do the extra practice sessions in Hogsmeade and see where they get you,” said Harry reasonably. “It’ll be more interesting than trying to get into a stupid hoop anyway. Then, if you’re still not—you know—as good as you’d like to be, you can postpone the test, do it with me over the summer—Myrtle, this is the boys’ bathroom!”