It's no secret that the Harry Potter films had to cut out many moments from the popular books. But one time-saving omission is particularly odd because it detracts from the understanding of the title. In Harry Potter and the Half-Blood Prince, Harry (Daniel Radcliffe) and his friend question the intentions of the self-proclaimed prince who once owned the potions book Harry found. With simplified potion recipes written in the margins, Harry slowly becomes enthralled by the mysterious Half-Blood Prince. But when he discovers dark spells written into the book, there are even more questions about the previous owner. Of course, the movie reveals the Half-Blood Prince to be Severus Snape (Alan Rickman) when Harry tries to use one of the dubious spells against the Death Eaters that killed Dumbledore (Michael Gambon), and Snape stops him, blocking Harry's sectumsempra spell and confirming his identity. But that is all the explanation given.