The answer to this question can be found in Chapter Three, in which Jack, in spite of his lack of success in hunting, reveals to Ralph and Simon the way that he is becoming obsessed with the hunt and the kind of violence that it involves. The "compulsion to track down and kill" is said to be "swallowing him up," as is made clear from the folllowing revelation:
"I went on. I thought, by myself--"
The madness came into his eyes again.
"I thought I might kill."
It is highly revealing that words such as "madness" and "compulsion" are used with reference to Jack and his desire to kill and shed blood, and also note the way that in response to this confession, Ralph himself, the boy who most represents the order of civlisation in his person, is said to feel "some hidden passion" as he responds to Jack, foreshadowing the way in which the blood frenzy will even overpower Ralph.
At the beginning of Chapter 3, Jack is crouched low to the ground looking for pig droppings in order to track them down. While Jack is attempting to hunt, Ralph and Simon are working by themselves on the makeshift huts. Unfortunately, Ralph and Simon cannot build sturdy huts because the other boys refuse to help them. When Ralph begins to complain about how the majority of the boys ran off to bathe or hunt, Jack responds by saying that the boys want meat. An argument then ensues between Ralph and Jack over the need to build shelters. Ralph also explains to Jack that the littluns are frightened and the shelters will help ease their minds. Jack reveals that he does understand the littluns' fears by saying,
"If you’re hunting sometimes you catch yourself feeling as if—...There’s nothing in it of course. Just a feeling. But you can feel as if you’re not hunting, but—being hunted, as if something’s behind you all the time in the jungle" (Golding, 73).