Half-Blood Prince

[Carol]

No: HPFGUIDX 183808

Pippin earlier:
> > >  Snape's association with Sectum Sempra was generally known.
Lupin declares that it's a specialty of his in DH. <snip>
> > 
Carol earlier:
> > 
> > That statement has always bothered me. Lupin didn't know, any more
than Sirius Black did, that Snape had been a DE, and Severus could not
have performed a Dark Curse that Madam Pomfrey couldn't heal at
Hogwarts without being expelled. (The little cut on James's cheek
doesn't count; clearly he was not "cut always.")
> 
> Pippin:
> But clearly it *is* supposed to count. Why else would JKR have had
Snape cause that particular injury? If I know anything about young
men, James would have been mortified to go to Madame Pomfrey over a
slight cut on his cheek. As for squealing on a classmate, he'd have
died first. 
> 
> Snape and everybody else who used the curse at Hogwarts was probably
just a lot more careful with it than Harry was, knowing that if they
did  permanent damage with it they'd be expelled. After all, a lot of
the magic they use could be damaging if mishandled -- you could stun
or petrify someone so they fell down the stairs or over a parapet, you
could poison them with any number of potions, and so on. 

Carol responds:
I don't agree. If James, who didn't know the countercurse to
Sectumsempra, had been hit with that curse, he would have kept on
bleeding till Severus Snape, the one person who did know it (assuming
that he'd invented it at that point--it was pretty complex) performed
it on him. The teachers would not have let him stay in class with a
permanently bleeding cheek. It would have been, "Hospital wing,
Potter!" And then Madam Pomfrey would have realized that the injury,
inflicted in front of the entire fifth year class, was Dark magic that
she was incapable of healing. And Severus Snape would have been expelled.

That little cut, which was not permanent and did not even leave a scar
as far as we know, may have been a precursor to Sectumsempra, but
there's no evidence whatever that it was Sectumsempra itself. Nor did
he cast the spell aloud; it was nonverbal, so neither James nor Remus
nor Sirius would have known what it was.

Stunning and Petrifying are not Dark spells that require elaborate and
secret countercurses that only Severus Snape knows. And it wouldn't be
a matter of "squealing on a classmate"; the entire fifth year class
was watching, and any of them could have told on Snape if doing so
violated MWPP's code of honor, such as it was.

Even a carefully controlled Sectumsempra (and Severus was rather too
furious for careful control--he made a slashing movement, IIRC) would
be "cut always" without that countercurse, just as there was no
restoring George's ear through Molly's Healing magic. (I'd like to
think that Snape could have restored it, but he never got the chance.)

You may be able to reconcile Lupin's remarks with the available canon.
I can't. It makes no sense to me--unless JKR forgot--again--what she
had actually written in previous books, just as she had the incident
occur at the end of fifth year but the spells are written in a
sixth-year book. (Yes. that can be reconciled, too, but only by
finding off-page possible solutions to an on-page inconsistency.)

Carol, who doubts that "everyone else" used a curse that Severus had
marked "for enemies" and would probably only have used in the DE days
that Lupin didn't know about until after the fact