Bucky was watching her closely, in case she made any sudden moves, so he didn't miss the change in expression. Something had upset her, maybe reminded her of something - she looked the way he felt, when he got hit with a flashback or a bad memory popping up.

"What?" His attention sharpened, and his brows drew together in concern. Then he kicked himself, because the problem was likely the obvious one. "Did you leave someone behind?"

Unlike him, most people would have ties to others, people they cared about, were worried about, who would be worried about them. Small wonder she'd be upset at the reminder of home.