"Mmmn," is his complicated response. He doesn't wince or flinch at the prodding, mostly because he's had far worse injuries that hurt way more — and at her instruction he shrugs and nods. He knows. Infection is bad. Takes arms and legs and all sorts of unpleasant things, out in the Wastelands. He's no stranger to it. As she looks, she may notice slight patches where his hair doesn't grow in — little nicks and cuts turned into scars; one is on the other side of his forehead, crossing into his hairline. Another thing she may notice is that his forearm has a clear burn mark, fresh but healed, in the shape of a hand.

He finally (surprisingly) adds in a low voice, "Can fell out of the sky."

You can put two and two together.