It's odd, but seeing Tony this tense is actually making Natasha relax. There's a level of tension in her that never truly goes away, a baseline thrumming through her body at all times. But the extra tension that's been making her shoulders and jaw ache ever since she crept into the workshop? That is slowly seeping out of her, making her features soften slightly. It doesn't take a genius to tell that he isn't comfortable with the situation, but despite that fact, he's staying put and trusting her. And it's oddly comforting not being the only one fighting to trust people here.

Her face goes blank at the words leaving Tony's mouth. Like most of them, she understands individually (except for dipole, what the hell is that?) but string them all together and she doesn't have the first clue what they mean. "Right," she says slowly, dragging the word out. "But what's it doing in your chest?"

Her eyes track Tony's finger as it traces a path along the rim of the... arc reactor. Her own fingers are itching to touch it as well, but she won't do it without his permission, or without knowing that it's safe, for that matter. She's never seen anything like it before. Who knows what it's capable of? Or how much it might hurt? In this case, caution is her friend. So, instead she presses her hand flush against Tony's belly, just by his belly button, thumb rubbing absently along a short, white scar. A solid touch is easier to get used to than the featherlight ones she's been giving him so far, and maybe that'll ease some of the tension out of him.