“The term, Mr. Potter, is Avada Kedavra,” Professor Quirrell’s voice sounded a bit sharp for some reason
Possible reasons include:
He was Voldemort, and has some reason which seems good to him for not trying to AK Harry, then or now. The reminder that at least one Outside View says otherwise annoys him.
He wants Harry to learn AK, well enough to ensure the boy casts it (or genuinely tries rather than trying to try) in a moment of crisis, and thus wants him to practice the actual pronunciation or at least not practice mangling it.
Though the “for enemies” event hasn’t happened yet, other events gave him a (possibly irrational) distaste for Muggle-borns who think “abracabara” is funny.
Possible reasons include:
He was Voldemort, and has some reason which seems good to him for not trying to AK Harry, then or now. The reminder that at least one Outside View says otherwise annoys him.
He wants Harry to learn AK, well enough to ensure the boy casts it (or genuinely tries rather than trying to try) in a moment of crisis, and thus wants him to practice the actual pronunciation or at least not practice mangling it.
Though the “for enemies” event hasn’t happened yet, other events gave him a (possibly irrational) distaste for Muggle-borns who think “abracabara” is funny.
A sharp tone serves his goals for some reason.