Just got to thinking the other day about some things . . . we see a lot of Levicorpus in DH . . . in HBP we see Harry learning of the spell in Snapes potion book, thing is, in OotP we see James using the spell against Snape (as well as Snape using Sectumsempra against James) OK, so here's the problem. Harry is seeing Snape and the Marauders as they leave the Great Hall after their OWL's that is at the end of 5th year, but it appears that Snape didn't create those two spells untill his sixth year . . . Is this just a glitch in JKR's chronology, or Was Snape perhaps a year ahead of others in potions classes?