Within ACL 3.2, the person pays attention to the effects caused by the back and forth motion. The held object causes an effect on another object, e.g. a crayon on paper. Back and forth is usually in approximately the same location, in a horizontal plane.
The reason for the abstract description is that once you learn to recognise the back and forth motion, you are not stuck with crayons and paper. You can offer pens, pencils, sand paper, soap, wash cloths, lotion, tooth brushes, etc. to be used on different surfaces. The motion and the conscious cause and effect connection between the object and the effects on the surface establish a pattern of performance.
Crayons and paper can be replaced by any objects that fit the description and appeal to the person. Flexible methods for engaging functional abilities are needed to accommodate individual and cultural differences as well as additional impairments with seeing, hearing and neuromuscular actions.