Michael and Vaughan in “Unfinished Business”

So why hasn't anyone tried taking one of them alive? [Vaughan gives him a look] All right. Dead, then. Undead. Whatever you call it.

They don't take prisoners.

What, so we're no better?

No. They're better. Stronger. Faster. Surprise is about the only thing we've got going for us, so forget about fair warning.