  :::This is clearly getting ridiculous.  Snape knew how to cure Scermptsa – a spell mentioned only in the HBP's book, clearly not a spell mentioned or taught in school.  Who would know it?  The creator of the spell, Snape.  He also knew about Levicorpus.  He is also extremely suspicious when he Slughorn praises Harry as a great Potion-maker, and knew that his old book was still in the cabinet.  Harry says it himself: Snape didn't say anything because he would trip up Dumbledore. :::The book is assigned to all sixth years.  We have no proof at all that Lily ever befriended Snape – we see her defend him, but Snape rebuffs her.  Lily calling herself a Half-Blood when she is clearly a Muggle-born?  And Prince?  That seems ridiculous.  The book also contians a lot of Dark Arts spells %ndash; Sirius says that Snape knew more curses in his frist year than half of the seventh years.  lily in the Dark Arts?  Not probabe.  