She means that as a threat, he figures. It sounds like a threat. Probably she doesn't mean for him to try to make any more of it than just that: I've killed before, I'll do it again.

(And he believes her, though for one reason or another he's not sure he buys that she'll kill him.)

It'd be one thing if she said what he figured happened: they got bit, she took care of it. And it's maybe like that, still, but what she says is what he's got to go by. It don't matter much, if one of 'em was bit, if both of 'em were. What she's saying is simpler, and it's something he understands too goddamn well.

(After all, he'd left because he figured it'd be easier on Daryl, not having the two of them at each other's throats every other night, but if his old man had hurt his brother-- well, he can't swear he'd do the same, but only 'cause time was there were consequences for killing a man. Even then. His temper then was maybe worse than it is now.)

"All right," he drawls evenly. He's guessing that's not quite the reaction she wants: a sort of grudging respect, but not a lick of fear. If she's hoping to send him off, tail between his legs, she'll have to work a lot harder.

"You plannin' to hang around here til you see 'em again?"