Today's Pottermore riddle unlocks the "Slughorn's Party" page of the Harry Potter and the Half-Blood Prince section at J.K. Rowling's Harry Potter website. If you recall from the book, the professor's very exclusive party marks the appearance of a vampire named Sanguini, who skulks around the party creeping people out. Rowling uses this installment at Pottermore to discuss the subject of vampires, including the revelation that there was almost a vampire professor at Hogwarts named Trocar, but she decided not to include him. From there, Rowling is very clear that Trocar did not evolve to become Severus Snape at some point in the character development process. When speaking of the fan rumors about Severus Snape possibly being a vampire, Rowling says:
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