His black eyes roved over their upturned faces, lingering for a fraction of a second longer on Harry’s than anyone else’s.
“You have had five teachers in this subject so far, I believe.”
You believe… like you haven’t watched them all come and go, hoping you’d be next, thought Harry scathingly.
“Naturally, these teachers will all have had their own methods and priorities. Given this confusion I am surprised so many of you scraped an O.W.L. in this subject. I shall be even more surprised if all of you manage to keep up with the N.E.W.T. work, which will be more advanced.”
Snape set off around the edge of the room, speaking now in a lower voice; the class craned their necks to keep him in view.
“The Dark Arts,” said Snape, “are many, varied, ever-changing, and eternal. Fighting them is like fighting a many-headed monster, which, each time a neck is severed, sprouts a head even fiercer and cleverer than before. You are fighting that which is unfixed, mutating, indestructible.”
Harry stared at Snape. It was surely one thing to respect the Dark Arts as a dangerous enemy, another to speak of them, as Snape was doing, with a loving caress in his voice?
“Your defenses,” said Snape, a little louder, “must therefore be as flexible and inventive as the arts you seek to undo. These pictures,”—he indicated a few of them as he swept past—“give a fair representation of what happens to those who suffer, for instance, the Cruciatus Curse” (he waved a hand toward a witch who was clearly shrieking in agony) “feel the Dementor’s Kiss” (a wizard lying huddled and blank-eyed, slumped against a wall) “or provoke the aggression of the Inferius” (a bloody mass upon ground).
“Has an Inferius been seen, then?” said Parvati Patil in a high pitched voice. “Is it definite, is he using them?”
“The Dark Lord has used Inferi in the past,” said Snape, “which means you would be well-advised to assume he might use them again. Now…”