Well, he was trying to spare Matt an interrogation by not actually asking the questions that were coming to mind, but if he's going to jump in. "How does it even work? I mean..." He stops and clenches his jaw, because he's not sure he wants to be That Guy and ask this question, but: "Are you actually even blind?"

And great, now he has Captain America giving him a disapproving look, and he wilts a little in the face of it.