The cue that captures attention is the effect that the hand produces, i.e. the effects of grasp and release. Cause and effect is experienced, evaluated, compared with prior experiences with producing effects and a choice is made about whether or not to continue producing the same effects, i.e. to continue to grasp or to release.
The traditional way of thinking about cause and effect misses the point as far as the person is concerned. The person has a choice. The choice is made in the context of past, present and the future cause and effect relationships.