All seven novels show Snape to be a very powerful wizard and to have been outstanding while a student. He specializes in potion making and has talent and passion for the Dark Arts. Sirius claimed that Snape knew more hexes and curses as a first-year student at Hogwarts than most seventh-years knew. Particularly gifted in potion making, Snape added major improvements to his potions textbook while still a student. Also as a student, Snape shows a rare gift for discovering new spells. Lupin describes Sectumsempra as Snape's "specialty" in Deathly Hallows. Snape is shown using this spell as a teenager against Harry's father James and in the aerial battle in the last novel when he accidentally hits George Weasley (acting as a Potter decoy) with it while actually aiming for a Death Eater who was trying to attack Lupin, permanently severing George's right ear. Despite Sectumsempra's deadly power, Snape can also heal the wounds it causes. Snape is adept at reversing or containing fatal damage from other dark curses as well, due to his vast knowledge of Dark Arts, as he does when Dumbledore and then Katie Bell are cursed. Skillful in the arts of Legilimency and especially Occlumency, Snape is able to both access the minds of others and protect his own thoughts—indeed, though Snape does not care for the term himself, Harry forms the uncomfortable impression early in the series that the Potions Master is able to "read minds." Being an Occlumens, Snape is able to keep his betrayal from Voldemort, who is himself described as being "the greatest Legilimens" in history. According to Rowling, Snape is the only Death Eater capable of producing a full Patronus, which, like Lily's, is a doe. Snape is a talented duellist, able to hold off by himself (if only briefly) a group of three Hogwarts professors that included former dueling champion Filius Flitwick. Professor McGonagall later implies that Snape learned to fly without the use of a broom, a rare skill previously displayed only by Voldemort.