Repulsed and revulsion: Harry, Snape and Dumbledore
In HBP, there are two scenarios where Harry and Snape were under Dumbledore’s explicit instruction. Their actions caused great harm to Dumbledore, but they each complied, as they knew it was necessary.
I love the comparison of how both characters are described in these two scenes. The juxtaposition is a great clue by Rowling as to Snape’s true role.
Harry and Dumbledore are in the cave, and Harry forces himself to do something that causes Dumbledore harm.
Hating himself, repulsed by what he was doing, Harry forced the goblet back towards Dumbledore’s mouth and tipped it, so that Dumbledore drank the remainder of the potion inside.
A handful of pages later, Snape is on the tower with Dumbledore, and Snape forces himself to do something that causes Dumbledore harm:
Snape gazed for a moment at Dumbledore, and there was revulsion and hatred etched in the harsh lines of his face.