Snape's an ass. A useful ass, some of the time, but mostly just an ass.

And don't try killing him. I don't know what your combat abilities are, really, but chances are you're not going to manage it. He can create illusions, sink into the ground, seal things closed, summon his children who like to tear into things with their teeth... I'd even condone the killing but I couldn't manage it.

...Shit. Do me a favor and forget I said I'd be fine with killing him, please?