She's been witness to shutting a machine that's doing something to Steve not working when it was shut down too soon. Even so, Natasha moves closer to the machine, her eyes darting between the scientist and Steve. Her gun never moves from the scientist, though.

"You're gonna be OK." She says so softly that no one will be able to hear her, even Steve. She has to be OK. He's Captain America, for God's sake. No...that's not why. She needs him to be himself again.

Two minutes until they get swarmed with Red Room henchmen, by the way.