Okay, I just finished re-reading the Half-blood Prince yesterday in preparation for my daughter and my midnight trip to the bookstore to buy “Harry Potter and the Deathly Hallows.“
I am now going to issue my one and only guess about Prof. Snape. (/drumroll)
I think Snape is loyal to Dumbledore in the end.
I believe that Dumbledore pleaded with Snape to kill him because if Dumbledore did not die, Draco Malfoy and his family would be killed by Voldemort. Snape, who had sworn an unbreakable vow to aid Draco, in acting in accordance with Dumbledore’s wishes both achieves the end result of his vow and keeps faith with Dumbledore.
The look of revulsion on Snape’s face was because he hated having to kill Dumbledore, the only person who ever finally believed totally in him.
Note that Snape very carefully avoids harming Harry Potter in the next scene and instead acts to protect Harry from the worst of his desire to act in revenge.
The loathing look on Snape’s face was probably a profound jealousy that he would never share the mentor-student relationship with Dumbledore that Harry had.
So in the end, Dumbledore sacrifices himself to save a traitor’s life. A profoundly Christian thing to do.
I guess if I’m right, I’d expect Draco to show signs of redemption as a result.
I’ll be back in about 36 hours to grade myself.
(Update: I’ve gotten my silver armbands and my tickets for the drawing at Borders tonight. My daughter is in a show that’s opening tonight, but the plan is that as soon as she’s out of costume and make-up we’re on our way to the book store. It took me until about 8 AM in the morning to read my way through the Half-blood prince. Let’s see if I can do the same with this book.)