What does ZigZag insist that Stanley take care of?

In chapter 17, the boys in Group D dig around the area where X-Ray supposedly found the gold tube for an entire week. One afternoon, the boys are digging in close proximity to each other when ZigZag's shovel accidentally hits Stanley in the side of the head. Stanley immediately collapses to the ground while the dirt on his shovel falls off. As Stanley is lying on the ground attempting to recover, ZigZag stands over top of him and tells Stanley that he refuses to scoop up his dirt that fell off his shovel.
After Stanley recovers and has the wound on his head bandaged, he returns back to the hole, where ZigZag is waiting for him. ZigZag proceeds to tell Stanley, "That's your dirt . . . You have to dig it up. It's covering up my dirt" (Sachar, 35). ZigZag then makes Stanley scoop up the small mound of dirt before he begins digging again. Essentially, ZigZag insists that Stanley take care of scooping his own dirt after he is injured. ZigZag's petty behavior emphasizes the hostile atmosphere of Camp Green Lake. Later on, ZigZag will start a fight with Stanley because Zero begins helping him dig his holes each day.