In The Half-Blood Prince, when Harry used the spell Sectumsempra on Malfoy, was Snape able to reverse the effects of the curse because he was the one who created it?

  • 7
    As the creator can Smith and/or Wesson revert a gunshot wound? Snape was skilled in dark magic and knew the construction of the spell, that gave him the knowledge which allowed him to treat the wound (when coupled with his existing knowledge of healing magics). It was only tangentially related to the fact that he created the spell.
    – Jeff
    Dec 19, 2019 at 23:50
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    @Jeff That seems too specific. A creator of a poison may well have ready knowledge of an antidote, and a creator of a computer virus may well know exactly how an antivirus for it may be written. Unless you can somehow demonstrate that creating a spell is like creating a gun, the gun example doesn't have a lot of weight.
    – Misha R
    Dec 20, 2019 at 7:11
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    @MishaR Those examples you've provided focus on stopping the force, but they do nothing to reverse the effects. Someone who is poisoned might receive the antidote which stops them from dying, but there might be irreparable damage that can't be reversed. Someone who creates a computer virus might be able to stop it from infecting more, but anything it's deleted or corrupted might not be reversible. I think it's reasonable like you suggest that Snape might know how to stop the spell, but the gunshot wound example is a lot closer to the question being asked because it's about reversing effects.
    – Davy M
    Dec 20, 2019 at 16:30
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    @DavyMwenttofundMonica My point was not that my exact examples work, it was that any example needs to be backed up. However, I also think the point you bring up is entirely wrong. There is nothing irreparable about the effects of Sectumsempra. It's a laceration spell. The human body has damage control capabilities, and the wizarding world has body-mending magic. So the physical effects can certainly be countered. The only way they cannot be counted is if there is magic in place preventing any healing - which is A. subject to a counter-spell, and B. is distinctly different from a gunshot.
    – Misha R
    Dec 20, 2019 at 19:07
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    @MishaR: George Weasley's left ear was cut off during Battle of the Seven Potters by Sectumsempra, it was discussed during the aftermath of that battle that curses wounds made by dark arts cannot be healed, and that's why George's ear cannot be regrown. Yet, Snape was able to heal Malfoy's wounds. It's not just "lacerations spell". My theory is that Curse and Counter curse presumably work like public key cryptography; it's possible to figure out the counter curse when creating the curse, but figuring out the counter curse independently is much, much harder.
    – Lie Ryan
    Dec 21, 2019 at 3:06

1 Answer 1


Snape reversed it using the counter-curse.

Snape reversed the effects of the Sectumsempra spell Harry used on Draco using a counter-curse. His success doesn’t seem to be related to his being the inventor of Sectumsempra - presumably anyone who knew the right counter-curse to cast and was sufficiently skilled at casting it could also reverse its effects.

“The door banged open behind Harry and he looked up, terrified: Snape had burst into the room, his face livid. Pushing Harry roughly aside, he knelt over Malfoy, drew his wand and traced it over the deep wounds Harry’s curse had made, muttering an incantation that sounded almost like song. The flow of blood seemed to ease; Snape wiped the residue from Malfoy’s face and repeated his spell. Now the wounds seemed to be knitting.

Harry was still watching, horrified by what he had done, barely aware that he too was soaked in blood and water. Moaning Myrtle was still sobbing and wailing overhead. When Snape had performed his counter-curse for the third time, he half-lifted Malfoy into a standing position.”
- Harry Potter and the Half-Blood Prince, Chapter 24 (Sectumsempra)

However, Snape likely was one of the few wizards who would recognize the effects of Sectumsempra, since he would be familiar with the effects of his invention and it was otherwise not a widely known spell. Therefore, another wizard might not have recognized its effects or known what counter-curse would reverse it.

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    It's entirely possible that nobody except Snape even knows the counter-curse. It would seem that one of the biggest advantages of inventing your own combat spells is that your enemies won't have their counters memorised; they'd have to work them out or reverse engineer the spell or however it's done, which presumably takes a level of skill and an amount of time. Dec 20, 2019 at 9:16
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    Is there actually any proof that Snape knew that it was Sectumsempra? Maybe he just did some generic deep-wound-healing magic. (He does refer to it as Dark Magic and “that spell”, but that doesn’t seem conclusive, especially given that he only says it after Harry reveals that he used a spell he didn’t know the effects of.)
    – Alex
    Dec 20, 2019 at 13:14
  • @Alex I think he guessed, since there aren't any other spells that give distinctive sword-like cuts in that way mentioned. Yes, there are cutting spells, but Snape was familiar with sectumsempra and probably immediately thought 'hey, that looks like my thing'. Feb 23, 2020 at 22:35

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