It's something called hypervigilance, when i looked it up, it said "the elevated state of constantly assessing potential threats around you" and i just thought, "hey, since asbu's an assassin she probably would have that, right?" because in the time period of the dragon world she lives in, instead of what modern assassins use, she actually has physical combat with her target most of the time, so she'd have to predict every move
One of the symptoms kinda fits with something i planned on having mullerian do in the prolouge to "the allignment," she's telling the story of everything that went on in the last few chapters of it (i'll get to writing those eventually i swear-) and she says "you could see the adreniline take over in her summer green eyes as her pupils thinned," and an article i found said that a symptom of hypervigilance was dilating pupils