Oh, Dean doesn't remember, but he starts to suspect. The way Sam won't meet his eyes any more. This one time he finds a chunk of skin that isn't his lodged under one of his fingernails. "Why don't we go out to a bar tonight, bang a few gongs?" he asks. Castiel doesn't look up from his workbench. Dean gets tired of waiting for an answer and goes to play poker with Sam and Meg.

Later in bed Dean asks, where did this scar come from, and this one, and this one? Castiel tells him they were just upgrades. "I'm trying to fix you," he mumbles into Dean's shoulder.