Dean. She had to bring up Dean. She was striking at so many different nerves right now. Sam honestly didn't know how to make all of the anger stop. She knew which buttons to push, where to aim, how to fire; every last detail that she needed to make him fall onto his knees was leveled at her advantage and he wondered how and when she had figured out what they all were.
"Don't," he started, voice uneven, "don't talk about that." Otherwise he would hit her. Without holding back, without thinking. Sam was pretty sure that he'd strike her so fast that even she would be shocked by it all. Dean was a big pressure point for him. Dean, the deal, every last bit of it. Having brought it up was a low play. Even for her, the way he saw it.