Why didn't Snape turn Harry in?

[Magpie]

No: HPFGUIDX 159153

I just finished re-reading HBP and the last chapter brought up a question--I hope it hasn't been brought up already.

The Trio is talking about Snape being the Half-Blood Prince and I think it's Ron who asks why Snape didn't turn Harry in when he realized Harry was using his old book.  I may be remembering it wrong (I read it earlier today but don't have the book in front of me now) but I think Harry even wonders if Snape suspected him of having the book much earlier, like after Slughorn praised Harry's Potions skills at the Christmas party.

Hermione says Snape didn't want Dumbledore to know about his own connection to the book and some of the spells in it, but that sounds wrong to me.  It's not like Dumbledore doesn't know the kind of kid Snape was, right?  He knows he was a DE, which was even worse--the book was before he worked up to as bad as he could be.  Snape's not Lupin trying to hide schoolboy indiscretions.  He's an ex-DE.

The fact that the question is asked, and Hermione's answer doesn't sound very convincing, and Harry himself says that he should have shown the book to Dumbledore because it was "proof" that Snape was evil at school "just like Voldemort" (Harry's even less objective about the book once he knows it was Snape's) makes me wonder if there is some more important reason Snape didn't turn Harry in.  Was there something in the book Snape wanted Harry to have?  Did Dumbledore know of it too and also want Harry to have it?  Was it information that Snape wanted Harry to have access to without Dumbledore knowing or agreeing?  Is there something in it that will help Harry later--Harry did make a point of hiding the book so he can still get it when he wants.  Was that scene only to give us a chance to see the Vanishing Cabinet was in the RoR, or will we return to it?

Or perhaps Hermione's explanation was right, but it sure didn't seem right to me--I especially doubt that DDM!Snape would be hiding something like that from Dumbledore. Or is there some obvious answer to this in the book that I've completely missed or forgotten?

-m

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