The image is of a monkey grasping fruit. This is a return of the symbolism to the monkey in stage three, but here his restlessness roaming has fixed for the moment on a particularly desirable object.
Clinging is an intensification of craving. It is the more or less obsessive quality of the mind which fixates on its object. There are said to be four kinds of clinging; sensual clinging, clinging to a an ego position, clinging to superstition (rites and rituals) and clinging to views (dogmatism.)
Clinging is the stage where we create a self-position. We identify ourselves as the possessor of the desired object. The intensification of the object creates a subject as its mirror-image.