Unveiling Snape's Ultimate Weapon in Harry Potter

In the movie, "The Half-Blood Prince," Hogwarts professor Minerva McGonagall assigns Harry Potter and Ron Weasley to take Potions lessons with the new teacher, Horace Slughorn. Unlike the previous Potions teacher, Severus Snape, Slughorn is a cheerful person who welcomes the duo to his class and promises to help Ron improve. During class, Harry discovers a tatty but annotated copy of Advanced Potion-Making that belongs to the mysterious Half-Blood Prince. Thanks to the Prince's annotations, Harry is able to brew a perfect potion and receives a vial of Felix Felicis as a reward. However, Harry's obsession with the book and use of a dark curse eventually causes trouble for him.

Harry Uses Sectumsempra on Draco Malfoy

Harry becomes increasingly fascinated by the Half-Blood Prince's annotated copy, particularly by a spell called "Sectumsempra." Despite Hermione's disapproval, he continues to study the book obsessively and refuses to let her or anyone else examine it. When Ginny Weasley takes the book from him and claims it as the Half-Blood Prince's property, Harry claims he is only curious about the book's previous owner but his actions suggest otherwise. Eventually, Harry discovers that Sectumsempra is a spell for enemies, and he plans to use it on McLaggen. However, in a duel with Draco Malfoy, Harry uses the spell without fully understanding its consequences, causing Draco to bleed profusely. Snape intervenes and saves Draco, leaving Harry horrified at what he has done.

Snape Invented Sectumsempra

In Harry Potter and The Half-Blood Prince, Harry unintentionally used the Sectumsempra curse on Draco, causing severe hemorrhaging. Despite claiming ignorance of the spell's effects, he was given detention with Snape every Saturday until the end of term. Hermione questioned the integrity of the Half-Blood Prince, while Ginny saw Harry's actions as self-defense against the Cruciatus Curse. As the movie nears its end, Snape reveals himself as the Half-Blood Prince and kills Dumbledore before escaping with Bellatrix and Draco. Harry, unaware of Dumbledore's plan, confronts Snape and attempts to fight him, but is ultimately unsuccessful.

Harry summoned all his remaining strength, rose to his feet, and bellowed, "Sectumsempra!" But once again, Snape deftly countered his attack, closing the distance between them before muttering in a despondent tone, "You have the nerve to use my own spells against me, Potter? Yes, I am the Half-Blood Prince." As it turned out, the meticulously annotated Advanced Potion-Making book belonged to Severus Snape himself, back when he too was a student at Hogwarts School of Witchcraft and Wizardry. What's more, it was Snape who had actually invented the vicious Sectumsempra curse, with the sole purpose of unleashing it upon his tormentors, the Marauders, who had relentlessly bullied him during his own time at Hogwarts.