"I didn't do anything!" Vala protested reflexively, without even stopping to consider what he was talking about. Let's be honest, it could be any number of things with her. She could name a few just off the top of her head, but she wasn't about to go and admit any of them until she knew exactly what he was referring to. And even then it was unlikely.

Reflex indignation done with though, her brain actually kicked in. "Wait, what do you mean exactly?" At least his accusatory tone was familar ground. Responding to that had successfully circumvented any emotion she was feeling. Which, when she discovers he doesn't remember ever being here before, will be a blessing in disguise.