She sees every little movement in the quiver of his hands and his fingers as he twists them softly together and apart, together and apart, together and apart, in a gentle dance of skittishness. He shifts gently from side to side, moving his weight from the ball of one foot to the other, in an almost unperceivable movement, but she sees it. His shoulders are hunched, and if he speaks at all, his lips barely move at all, and his nervous, tender nature is permeable.
She sees it all.
She sees the twinkle in his eyes when Tony Stark is crude, the twist of his lips when Steve is lost in modern day references, the gears of his mind churning when Thor says something well and truly alien.
Natasha sees Bruce, a puppet tightly bound by strings, controlled by the Other Guy, his movements slight and constrained - she sees how much he fears himself, and straying from his careful routine of serenity and despite everything she has ever learned about men and their testosterone addled minds, she cannot understand how this man, Bruce Banner, could lose his temper.
Could even lose his temper, never mind become a being whose temper is at his core.
And yet, in those rare instances where he has to clench his fists and leave the lab to breathe slowly and deeply, as some monks in Calcutta taught him before she dragged him into this environment which causes him constant vexation, she sees it.
A twinge of green in those dark eyes, deep and primal, a shadow of who Bruce Banner truly is and yet everything he was ever meant to be.
She starts, briefly wondering how long she has been studying him, and carefully arranges her features into an expression of nonchalance, an eyebrow rising.
His twist of a smile is there, the twinkle in his eyes present too.
He watches her a moment longer, before shrugging his shoulders and letting out a short laugh.
Her back is rigid, her hands clenched into fists, under the table, out of his sight, her face carefully expressionless.
But he sees her.
He sees the strings that hold her bound to SHIELD and Fury, perhaps not against her will but still, it would be better not to have a ledger dripping in gore in the first place. He turns his back to her, fetching something from his work bench, picking through bits and pieces of detritus left behind by Stark. He finds what he is looking for, and turns back to the bench she is sitting at, quietly watching.
His eyes lift for a moment from his work, and they meet her own, dark and full and soft. She smiles at him. He returns the curve of her lips, slowly and for a moment she sees nothing but Bruce Banner, hale and whole and complete with just an utterance of an incredible Hulk.
For that moment, they are nothing resembling puppets and they are small and insignificant and Natasha pins it down in her mind, another layer to cover the Red Room.
For the first time in as long as she can remember, she feels her heart twinge.
And he sees it.
I have no strings to hold me down, to make me fret or make me frown, I had strings but now I'm free - there are no strings on me.