Drudgery of the everyday. There's really nothing else to explain it. Banality of sadism. John, standing at the dump, Alka Seltzer pill wrapped in a piece of bologna for the birds. Has he ever thought what a bird might feel while its innards explode? That's not really the point. He wants to know if it can work. If he can leave a wake of destruction with nothing but everyday objects.
He watches the bird gulp down the bologna and retake flight. He sees it hesitate, and pop, it falls from the air, guts hanging out of its mouth.
Adam, working on the dock, sees all this and feels a sudden urge to throttle John or to throw him in the river. He grabs him by the arm, instead, and hauls him out of the dump, toward town. He wants the boy to suffer, but he doesn't have any options; the boy will not answer questions about his name, or where he lives. Instead, Adam kicks from behind and sends him lurching off into the street. John plots his revenge for a while, but doesn't follow through. John will probably be very successful.