The Harry Potter Fan Theory That Has Fans Looking Closer At Professor Slughorn

We're first introduced to felix felicis in Professor Slughorn's potions class in Harry Potter and the Half-Blood Prince, where students like Romilda Vane and Katie Bell are working to create the perfect potion. As Hermione (Emma Watson) explains, its other name is liquid luck — although translated from boring old muggle language Latin, felix felicis actually means luck's luck or happy luck — J.K. Rowling isn't the only writer who loves a Latin reference. In the movie, Slughorn explains, "One sip and you will find that all of your endeavors succeed — at least until the effects wear off."

We get to see this in action when Harry (Daniel Radcliffe) uses the potion against Slughorn to find out what really happened when he discussed horcruxes with Tom Riddle. It certainly makes Harry — or, as he puts it, Felix — extremely confident, and helps him track Slughorn down. But in the end, it's a combination of two old-fashioned muggle forces — alcohol and guilt — that push Slughorn to confess. Interestingly, in the books, Harry saves some of the potion and later gives it to Hermione, Ron and Ginny. But in the movie, he glugs down the whole vial — far more than the sip Slughorn mentioned in class. It's possible to have too much of a good thing.