Despite how casually he leans on Natasha, Bucky tenses up just a little at Steve's arm wrapping around her to rest on him. The change isn't something that would normally be very noticeable, but Steve should be able to feel it this time.

He might've been able to safely curl up with his friend for warmth once upon a time, but now it's almost too much to ask.

It only lasts a second, and then Bucky's making himself relax again. "She's out," he murmurs, not just to impart the information, but to take attention away from his own reaction just now. "And she sleeps soundly, believe me. But I'm worried. She shouldn't be this cold and tired."