"Sirius." She doesn't like this, having to put herself between her cousin, whom she likes, and this man who she feels she ought to at least defend -- but she'll do it, because it feels as if it's the right thing to do. It might've been easier for her to let him walk away with that little ampule, but she suspects that Snape won't tolerate it and she's not going to let this situation explode again when it seems like it's finally starting to calm down.

"Please be so kind as to deposit that back where it belongs on your way out." Prove to me you're better than this, she doesn't say -- because saying it out loud leaves more room to be disappointed, and she'd been around her family long enough to know that disappointment was something they did well. She'd given her family her full share of it running off and marrying Ted, and she was sure she'd failed them many times before that in their eyes.

She glances to Severus briefly, brow arched at the sulky teen look. "I swear to Merlin, if I have to bind you to your bedframe for a week so that you don't undo someone else's hard work of not letting you die, I will."