It's the noise that finally breaks Tony out of his I'm-fucking-working trance, making him spring a solid six inches into the air—he knows exactly what Given the Dog a Bone is supposed to sound like (he's heard it five times so far today), and to the extent of his considerable knowledge, Phil Rudd wasn't having a cymbal-throwing fit when he recorded the song. He pretends that it isn't a shock to look up and see Bruce fumbling with a line of test tubes that refuse to cooperate and just stay up on their rack, instead focusing intently on the code he's been trying to fix while his heart returns to a more normal rate.

Back in Black has just started when words manage to claw their way out of his throat. Bruce has apparently given up on the test tubes and is leaning his elbows on the table, rubbing his eyes beneath his glasses. He wants to make a casual comment about how exhausted Bruce looks (which isn't anything new, admittedly, and Tony can't help but think that it's twice as bad that he always seems this ragged), but what comes out is a snicker and a light jibe about how Bruce can't even match the tubes to the right rack. Bruce fires a comment back, and the words hang in the air for a long while.

For some reason, Bruce and Tony always seem to find the same lab at the same time. Some days the interaction is kept to Tony blaring the Clash and Bruce quietly asking JARVIS to turn it down, which goes in a maddening loop through the day but keeps them both awake enough to do what they need to. Other days—better days, really, for both of them—they're just about working on top of each other, managing to get equally involved with each other's projects as they are with their own. The best, hands down, are the ones when Tony doesn't have anything of vital importance to work on and hops onto the table beside Bruce, keeping a running commentary on every result.

It's easier talking to Bruce than it has been with anyone else in a long time. This might be, in part, because he's relatively certain that Bruce won't shrug him off like so many other people in his life are wont to do. It's not like he has many other places to go—essentially, he can stay in comfort and safety or run like a hunted animal, sleeping outside and stealing what he needs to survive. The choices are less than optimal, and the tiny part of Tony (the larger part, really) that is about as self-assured as a high-school geek with a stutter and headgear can't help but feel a sick sort of relief for that. If nothing else, he isn't likely to drive Bruce away any time soon because he has a horrible personality.

The neutral ground and daily exposure slowly but surely shrinks that weak, selfish part of Tony's mind away and replaces it with a calm sort of confidence, chipping away at his insecurities to replace them with something brighter. It only takes two or three weeks before he stops being hyperaware of where his limbs are at any given moment. His stance opens a little, which he doesn't think Bruce notices, and he does things like putting a hand at the small of Bruce's back when leaning across him for something, which he thinks Bruce probably does. A few days after that, the relaxed banter he has with his bots shifts to include Bruce—a miscalculation causes a volatile reaction in the solution Bruce is trying to make and Tony asks if he needs to grab one of the interns to give a crash-course on how elephant toothpaste is made while they clean it up, because clearly Bruce's sloppy mess isn't nearly foamy enough. It isn't much, but it's a step in the right direction.

Bruce, for his part, seems to realise the quiet difficulty Tony has with people. He quickly takes to keeping a watchful eye on Tony while they're out of the lab, steering conversations when he picks up on too much discomfort. The fact that he's coming to know the engineer well enough to spot the signals (the tremble-twitch of his fingers, the shoulders held too rigid, the clenched jaw, the arms crossing over the arc reactor) is a kick in the gut in and of itself. It's been years since he's been this close to someone, and Tony somehow snuck right into the aching wound in his chest with nothing but a nod to acknowledge that yep, I'm here and your sorry self couldn't get rid of me even if you tried.

He likes to think he's helping Tony—Bruce needs to rescue him less and less these days, and sometimes it's as easy as stepping a little closer for silent support before Tony is breathing again and the tension melts off. Maybe it's his own desire for company, but the way Tony's eyes scan for him every so often, as though to reassure himself that Bruce is still right there, seems to indicate that they need each other in equal amounts. It may not be the healthiest relationship in the world, but who are they kidding? Neither one of them is anywhere close to emotionally stable; pretending that they've both got it all together is an exercise in futility (a Navy SEAL-level exercise, mind you, not one for the average PE class).

It works for them, though. Their broken edges are knitting together, making one entity of Bruce-and-Tony, of Tony-and-Bruce, rather than just being the fractured pieces of two fractured men. The day will come that the mutual wounds will need flexing, when Bruce will need breathing room and other people to lean on, when Tony will need to face his social phobias without the training wheels, but for right here, now?

They're both happy to leave things as they are and to simply coexist.