Although the fire on the mountain that kills the boy with the birthmark at the end of chapter 2 could be seen as the beginning of the boys' loss of innocence in Lord of the Flies, Golding uses chapter 3 to further develop the downward turn of life on the island. Jack's obsession with hunting, the growing conflict between Jack and Ralph, and the fear the boys experience all reflect the boys' loss of innocence.
At the beginning of the chapter, Jack is tracking a pig. Interestingly, Golding compares Jack to an animal, showing how he is beginning to lose his humanity. He tracks the pig "dog-like, uncomfortably on all fours," and when a loud bird's cry startles him, he becomes "less a hunter than a furtive thing, ape-like among the tangle of trees." Jack swears when the pig gets away from him. He tries to explain to Ralph "the compulsion to track down and kill that was swallowing him up." He even finds it hard to remember what rescue is. Jack's obsession with hunting reflects his loss of innocence.
Jack and Ralph seem to get along fairly well in the first two chapters, but in chapter 3 they become "two continents of experience and feeling, unable to communicate." This rift also reflects a loss of innocence among the boys. Ralph complains that the other boys haven't helped with the shelters, and he chides Jack for not getting any meat yet. Ralph wants to "explain how people were never quite what you thought they were," displaying new-found disillusionment.
Finally, the fears of the boys show a loss of innocence. In a perfect place, they should have no fear, yet the littluns, and even some older boys, "talk and scream" at night. They fear a "beastie" or a "snake-thing." Even Jack says that when he's hunting he sometimes feels like he is being hunted, as if something is there in the jungle. Snakes and fear are part of the Garden of Eden account in the Bible; the snake tempted Eve to sin, and after she and Adam sinned, they were afraid.
Thus Golding uses Jack's obsession with hunting, the conflict between Jack and Ralph, and the boys' fear to portray the loss of innocence of the boys on the island.