I love the imagery here, and the close and careful way you've described Charlie's body language, and Don's observation of it. I think that TPTB aren't all that comfortable with the maybe-autistic reading of Charlie, perhaps because they want to have him be both genius and hot, and this twitchy oddness doesn't jibe with hotness, at least not in their minds, though y'know, I'm more than willing to believe in this Charlie (and hey, to lust after him as well).

One thing that I liked very much here was Don's guilty irritation with Terry's assumption he would be complicit in "the look," especially because, in canon, Don seems very protective of Charlie, yet regularly mocks him himself (especially with Alan around to approve of, and perhaps supervise it, but also when Alan's not around). That's pretty common among brothers, especially ones as competitive as Don and Charlie. And given Don's many reasons to resent Charlie, it made the perfect beauty of your string imagery taut and fragile, so that I was glad that Terry was there to bring out that protective instinct, because I kept thinking about how otherwise, Don would inevitably say something stupid, and thus accomplish exactly what he most fears, pushing Charlie away.

Oh, and as a Charlie/Larry fan? The string made me squee a little, happy squee.