Throughout most of chapter 3, Golding juxtaposes Jack and Ralph. Describe how he does this and what becomes clear about the two boys in these passages.
Chapter 3 opens with a detailed description of Jack hunting. At times, this description makes Jack seem more like an animal than a civilized young man. He is becoming more prone to and interested in violence and his demeanor reflects this. Jack "breathed in gently with flared nostrils, assessing the current of warm air for information. The forest and he were very still." Jack breathes the air in like a predator or a dog. He is compared to the forest, not so much in the sense of being peacefully in tune with nature, but rather in the sense that he is becoming more primitive, more like a predator, sniffing the air as an animal would.
Jack misses the pig and the scene transitions to Ralph who is doing something quite civilized: building shelters. This is a clear juxtaposition of the boys going/thinking in opposite directions. Jack is becoming more volatile and primitive while Ralph is clinging to notions of civilization.
Ralph complains that not enough of the boys are helping with the shelters. Jack only wants to think about hunting. Ralph asks Jack for help and Jack just replies "We want meat." Ralph also repeats the necessity of keeping the fire going; Jack is annoyed, as if he's more interested in killing a pig than being rescued. Golding stresses the difference between Jack and Ralph, calling them "two continents of experience and feeling, unable to communicate."