The Heart, the Head, the Mouth...in that Order.
The words are there, I told her, in the script. They have given to her by a paid wordsmith, the writer. The story and the intellectual meaning have been well mulled over and moulded by you, the writer (and the producer and the director soon to be shaped by the film editor). What is not explicitly given on the printed page, and what you should be primarily concerned with, are the specific and complex human feelings that move any human head to activate the brain to choose the words that you as the character speaks. That is the primary task of the actor: to have activated within her the emotions that motivate the brain to choose the words to say to the other characters.
The heart--emotion--is the domain of the actor.
Acting is an experiential activity, not analytical. "Think before you act; think after you act; but when acting, just live." The actor who does not allow his or her real feelings to fuel her verbal and intellectual fire is a cold actor, a dead actor, a non-actor.
The actor's task is to experience--in truth, to re-experience, to re-live--those emotional experiences that have been unique to the actor in the actor's past; and, once allowed to be re-lived on stage or on set, regardless of the particular script, become the universal emotional embodiment of human truth that underlay all human experience...scripted or otherwise.
In acting, it is the emotion felt by the actor thinking the thoughts and saying the words that moves audiences, not the thoughts and words themselves.