What are voluntary actions?

“She bent her finger and then straightened it. The mystery was in the instant before it moved, the dividing moment between not moving and moving, when her intention took effect. It was like a wave breaking. If she could only find herself at the crest, she thought, she might find the secret of herself, that part of her that was really in charge. She brought her forefinger closer to her face and stared at it, urging it to move. It remained still because she was pretending… . And when she did crook it finally, the action seemed to start in the finger itself, not in some part of her mind.”

Ian McEwan — Atonement