Sebastian has no issue with killing, of course, and right now every protective, possessive instinct in his being is screaming at him to stalk after Spike and make very sure he won't ever cross his line of vision again.
Ah... it's tempting, but he's not about to give up on his self-control just because a rude, entitled child thinks he has any chance of stealing anything that belongs to Sebastian. A Phantomhive butler kills on his master's orders, not beyond that. Sebastian remains where he is, letting Spike back away as he pleases.]
Do keep what I said in mind. I appreciate the light, by the way.
[Oh- and for that matter, speaking of murderous butlers, Sebastian realises there's a certain someone else he should make sure has no funny thoughts about Ciel, and that someone truly ought to take precedence. Torch in hand, he turns and leaves.