The spell that Snape used to heal Draco's wound wasn't a spell that would heal ANY wound. It was a Counter-Curse to the Sectumsempra curse… so could only heal wounds caused by that spell. Hermione couldn't heal the wound she gave Ron by Spliching him when she Apprated herself, him and Harry in an emergency.
Vulnera Sanentur was the song-like incantation of a healing spell which was used to heal deep wounds, which could also be used as the counter-curse for the curse Sectumsempra.
Minor wounds inflicted by this curse can be cured by the song-like incantation Vulnera Sanentur; the first usage eased the blood flow, the second caused the wounds to knit and the third removed the worst effects of the curse.
He promised to protect Draco Malfoy from harm and guide him whilst he attempted to perform the task the Dark Lord had asked him to do: to kill Albus Dumbledore. Snape was actually a double agent working for Dumbledore, who requested Snape to kill him anyway to spare him of a painful and humiliating death.
Sectumsempra is a curse invented by Professor Severus Snape, during his childhood, when he was known as "The Half-Blood Prince". He created it with the intention of using it against his enemies, and it soon became one of his specialties.
The REAL Reason Snape Created Sectumsempra - Harry Potter Theory
Is Sectumsempra a unforgivable curse?
There is likely a good reason that the Sectumsempra is not an unforgivable curse. It's mostly because Sectumsempra is Snape's personal curse that he created. It is not a widely known or used spell, and it is one that he kept secret — which means it can't be added to the list since no one really knows about it.
Vulnera Sanentur was the song-like incantation of a healing spell and counter-curse to the Sectumsempra Spell, which was invented by Severus Snape. While sectumsempra was invented by Snape, Vulnera Sanentur is often mistaken to be invented by him as well.
Despite her beliefs and her family's close ties to Lord Voldemort and the Death Eaters, Narcissa never joined the organisation herself, nor received the Dark Mark. While she treated most people coldly, Narcissa was very loving towards her family as well as devoted to them.
Malfoy spots Harry and casts a Cruciatus curse; Harry, defending himself, using the Half-Blood Prince's Sectumsempra spell without knowing its effects. To his horror, it gashes Draco's face and chest, spilling his blood everywhere. Moaning Myrtle flies off, screaming.
Draco is in his own house. He is his godson and the child of his good friend Narcissa and fellow former death eater Lucius. He is fond of Draco if you could call it that. He doesn't like Harry at all.
George Weasley and Remus Lupin arrived next, and Molly attempted to heal George's wound; he recovered, but his left ear could not be healed because the wound was caused by Dark magic.
While Severus Snape was trying to cut the hand of a fellow Death Eater, he accidentally used a Sectumsempra Curse to slice George Weasley's ear. This dark magic spell, which Snape created during his student years at Hogwarts, is a curse that slashes through the skin like a sword and causes great bleeding.
When Harry critically injured Draco Malfoy with the Sectumsempra curse, it was actually enough to have him expelled, as Professor Minerva McGonagall stated Harry was lucky not to have been, due to Snape giving lenience to prevent others from finding out that he was the one who invented the curse.
Family. Snape's family background is mostly shown in flashbacks during the course of the last three novels. Snape was born to Eileen Prince, a witch, and Tobias Snape, a Muggle, making him a half-blood (hence the name, "Half-Blood Prince").
He grabbed the group in the cellar and disapparated just as Bellatrix Lestrange threw a knife at them, which hit Dobby in the chest, killing him. Some viewers that this moment meant that Dobby broke his promise with Harry, but he never technically agreed to the wizard's wishes.
In the final movie, Harry Potter and the Deathly Hallows pt. 2, Molly first hits Bella with a spell that freezes her, most likely Petrificus Totalus. Then, she launches another one that shatters her entire body into pieces, which could be expelliarmus, bombarda, stupefy, or any spell that can produce such an effect.
Harry Potter's use on Draco Malfoy in the Duelling Club. The Tickling Charm (Rictusempra), also known as the Rictusempra Charm, is a spell that causes a victim to buckle with laughter. It also has at least two other side effects on the victim. It is usually used as a diversionary tactic in duels.
The spell requires controlled use, which implies practiced use, and after slicing up Draco the way he did I doubt Harry made much if any use of Sectumsempra. He's not especially bloodthirsty and may never have realized that it could be used with finesse, so he wouldn't have much use for the spell.
During this year, Narcissa became pregnant and miscarried. She was distraught and uncertain of what to tell Lucius, as she had not told him of her pregnancy. Shortly thereafter, he brought her out to the Leaky Cauldron to visit with his friends Vettlingar Yaxley and Thorfinn Rowle.
She married Rodolphus Lestrange after leaving Hogwarts "because it was expected of her" to marry a pure-blood. However, Rowling stated in an interview that Bellatrix truly loved Voldemort.
He marries Narcissa Black and together they have one son, Draco, who is the first Malfoy family member introduced in the series. The Malfoys are related to the Black family through Narcissa (a first cousin of Sirius Black, Harry's godfather), which makes Draco a nephew of both Bellatrix Lestrange and Andromeda Tonks.
Harry yells “Sectumsempra,” the hex scribbled in the margins of the Half-Blood Prince's book. Blood spurts from Draco's face and chest, and Myrtle beings screaming. Snape bursts into the room and heals Draco's wounds almost immediately. Snape hurries Draco to the hospital wing, commanding Harry to wait behind.
As vile as this fight was, the question remains whether Snape gashed James' face using Sectumsempra. The short answer is no. While yes Snape did gash the side of James' face, Sectumsempra is a far deadlier curse.
Yes, he did. Against Severus, who blocked the spell. Or curse, if you prefer. The excuse Harry had for using it the first time “I didn't know what it could do" can't be used to justify his use of it a second time, when he knew full well what he could do.
