Continuity mistake: How can Ron and Lavender be in a 'prominent corner' of the Common Room when in Harry Potter and the Philosopher's Stone, it says it is a circular room?
Continuity mistake: On page 186 of the American hardcover, about a quarter of the way down the page, a paragraph begins "Malfoy looked rather as he had done the time Hermione had punched him in the face." However, Hermione never punched Malfoy in the books, she slapped him in Book 3. She only punched him in the third movie.
Continuity mistake: When Severus talks to Narcissa and Bellatrix in his house, he states that he "had sixteen years of information" about Dumbledore when Voldemort returned. However, Voldemort returned in June 1995. Snape would only have been teaching at Hogwarts (and supposedly spying on Dumbledore) for not quite fourteen years at that point, as he started in 1981.





Answer: The other answer is spot on, but I would add that it requires casting a specific spell while simultaneously killing someone to make horcrux and split one's soul. (The movie downplayed this and the spell name is never revealed in the book.) Professor Slughorn had told the young Tom Riddle that the act involved dark magic, though he did not provide details. Riddle apparently discovered what that dark spell was to make horcrux.
raywest ★