When Harry, in the cave, is making Dumbledore drink that potion he was -Hating himself, repulsed by what he was doing, Harry forced the goblet back toward Dumbledore's mouth ...(HBP pg 571/534)

Now, notice any similarities to this?

Snape gazed for a moment at Dumbledore, and there was revulsion and hatred etched in the harsh lines of his face. "Severus... Please..." (HBP pg 595/556)

Revulsion and Hatred. Both Snape and Harry hated what they were doing. I already supected that, but it's interesting to note that JK used almost exactly the same wording to hint at this.


Also, at Dumbledores funeral, the body burst into flames.

Remember in PoA when Harry was doing his homework, he had to read about Medieval Witch Burnings?

Non-magic people (more commonly known as muggles) were particularly afraid of magic in medieval times, but not very good at recognizing it. On the rare occasion that they did catch a real witch or wizard, burning had no effect whatsoever. The witch or wizard would perform a basic Flame Freezing Charm and then pretend to shriek with pain while enjoying a gentle, tickling sensation. (PoA pg 2/7)

I don't think I need to explain any further.