Subset of an autism headcanon but I think he gets noticeable tension in his wrists when he's overstimulated that make him wanna rip his arms off but since he's vowed to take good care of his hands he kind of just has to bite something really hard and pray instead of stimming as aggressively as he would want to to get it out of his system. Bonus I think Niji also gets like that but since he doesn't particularly GAF he does snap his wrists around like he's aiming to break them.