In the moment of her sharpness Seth thinks of thing prehistoric in nature. Not the creatures that went extinct, no, but the ones who never needed to learn how to adapt a second time. If he felt like ladling on compliments he'd say it's fetching, but as it is he decides to hold onto it in case he has a need for compliments in the future. If she's offended it'll tell him a thing or too about her, just as it will if she isn't.
Anna, for her part, can enjoy the look Seth gives his maimed hand--it's not apprehension, but anticipation, like a child looking forward to a particularly rare treat. He's even smiling with half-closed eyes as he unwraps as much of the towel as will go easily, knotting it in the fingers of his left hand, and he takes a shallow, easy breath before he rips it clear in a sharp jerk.
"Motherfucker," he says, with a half-sob that almost pays as laughter (but Seth never laughs) as fresh blood gouts from the reopened wound, and he puts the towel underneath it to capture it. His severed bone flashes out of the stump as he watches it with pained delight, and it takes him a little while to remember that he should be directing his hand towards the sink. He does it then and smiles serenely at Anna, still quite pleased with himself, and crooks his eyebrows.