"revulsion and hatred etched in the harsh lines of his face"

[tbernhard2000]

No: HPFGUIDX 135313

So, this is evidence of many things, in fandom at any rate - most
notably that Severus is furious at having to follow Dumbledore's
expectations, or that he is gathering hatred at Voldemort to
accomplish the deed, or he doens't think of Albus at all, only Draco's
wilting, or that he is repulsed by Albus' weakness, his victim state.

Wait, did I make up the last one?

But that's the only explanation that really, honestly, makes total
sense this way, considering what we know about both of those
characters. It's what came to my mind reading the passage first time
through. At any rate, the meaning of that revulsion and hatred is key.

I haven't read an entirely convincing, Snape-based explanation for it,
is all I'm saying. 

However, when Snape says the Potter is for the Dark Lord, I also hear
him saying, "forget Potter, he's irrelevant to us right now," and
underneath that, I hear "the Dark Lord is for Potter." So, I'm as
ambiguous as the rest here.

Nevertheless, the revulsion and hatred needs a real explanation, not a
rationalization.

dan