His expression softens from the more business-like I-am-explaining-a-theory face he had when she does that. It looks like she's protecting herself from something and he's not exactly unfamiliar with the pose.

"No. It wouldn't."

While it might be possible, it's so unlikely he might as well agree.

And once again there's the silence that says that she's free to elaborate on that, if she feels like it. If she wants to. Because it sounds like there might be something else behind her words, and even if there isn't, well - he's got nothing pressing to say in this exact moment anyway.