Chapter Three of Lord of the Fliesfinds a crouching Jack with a sharpened spear sniffing the ground; then, when a bird screeches, Jack shrinks back, hissing as though he is a "furtive thing, ape-like among the tange of trees." Still bent, Jack seems to begin his degeneration into a more primitive being than the civilized boy in the choir robe who first arrived on the island as he looks down at the trodden ground for evidence of a pig.
Clearly, Jack has become consumed with hunting. He himself tells Ralph that he has to go on after the other hunters have returned.
He tried to convey the compulsion to track down and kill that was swallowing him up.
As he attempts to explain to Ralph that he has thought he could kill a pig, there is a "madness" that comes into his eyes as he speaks. His repetition of the phrase "we want meat" is indicative of this overwhelming compulsion to track and kill pigs.