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.
It is pertinent to mention that Harry only knew Sectumsempra was for enemies and that to him, was reason enough to use it in his duel with Draco Malfoy that took place in the boys' bathroom.
Why did Harry not get in trouble for using sectumsempra?
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.
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.
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.
Harry Potter and the Half-Blood Prince (1/5) Movie CLIP - Harry vs. Draco (2009) HD
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.
Severus Snape used this spell to save Draco Malfoy after he was attacked by Harry Potter using Sectumsempra. He then took him to the Hospital Wing for further treatment, hoping to avoid scarring.
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.
What was Snape's reaction to Harry using Sectumsempra?
Later that night, after Snape killed Dumbledore, Harry attempted this curse against him multiple times, only for Snape to block it repeatedly and angrily reveal to Harry that he was its inventor.
It's implied that Septum Sempra is Snape's own creation, that he used a specific counter-curse to heal Draco, and that the spell isn't designed to be instantly fatal, but to inflict a gruesome, but relatively slow death if left untreated. It's likely Snape is the only person who knows said counter-curse.
The injury was caused by Snape's Sectumsempra spell in order to stop the Death Eaters from hurting George (who he thought was Harry) and Lupin, but missed and hit George. Hermione and Kingsley then arrived, both unharmed, followed by Arthur and Fred Weasley, both concerned for George.
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.
It is this misguided belief that motivates Voldemort to act as he does. The film differs from the book in its portrayal of the method used to kill Snape, but neither uses the killing curse for the simple reason that the Elder Wand is said not to be able to act in direct opposition to its master.
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.
Though the aforementioned healing spell may heal the wounds and dittany may prevent scars, any body parts that have been severed by this curse cannot be grown back (a trait of dark magic's permanent effects), as demonstrated by George Weasley when he had his left ear cursed off due to the spell.
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.
Throughout the 1996–1997 school year, Draco Malfoy would go to the washroom to find company with Moaning Myrtle, confiding the stress of his mission and fear of failing it.
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.
Not as fast lethal as unforgivable curses like AK but just a tier down. The sectumsempra spell is used to make a cut through a persons body. If the curse hits your torso you will start bleeding like it happens to Draco Malfoy when Harry uses the curse on him in Half Blood Prince.
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.
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").
Having gone through the horrors of the second wizarding war as a Death Eater, Draco abandoned the pure-blood beliefs he was originally devoted to, and grew to become a better person than he was in his youth, growing more tolerant and accepting of the non-pure-bloods of the wizarding world.
In Harry Potter and the Deathly Hallows, Fred and George are members of the Order of the Phoenix and serve as two of Harry's six decoys when he escapes Privet Drive. George loses one of his ears to Snape's Sectumsempra curse (which was aimed at a Death Eater's wand hand, but missed).
