Key to Jack's success as a hunter is his "discovery" that the pig's "don't smell me. They see me, I think. Something pink, under the trees." To the sadistic Roger, Jack explains, as he smears clay on his face, that they need to appear to look like something else--"Like moths on a tree trunk." Golding writes that "Roger understood and nodded gravely."
Jack's desire to dissemble his savage intentions are evinced in Chapter Three with his discussion of how to hunt the pigs, for "Now the antagonism was audible." As an indication of Jack's descent into savagery, he puts his "nose to the ground," only a few inches from the humid earth, he moves in an "ape-like" manner, hissing in the air, and squats,"streaked with brown earth," while holding his spear that is a sharpened stick, and wearing his knife-belt.
The third chapter starts off with an excellent description of Jack and how he hunts. To me, you can see everything you need to in the second paragraph:
Jack crouched with his face a few inches away from this clue, then stared forward into the semi-darkness of the undergrowth. His sandy hair, considerably longer than it had been when they dropped in, was lighter now; and his bare back was a mass of dark freckles and peeling sunburn. A sharpened stick about five feet long trailed from his right hand, and except for a pair of tattered shorts held up by his knife-belt, he was naked. He closed his eyes, raised his head and breathed in gently with flared nostrils, assessing the current of warm air for information. The forest and he were very still.
What is key to identify here, and what I am guessing your question is really about, is how, since their arrival on the island, Jack is becoming less "human" and more "animal" as is reflected in his hunting. He relies on senses such as smell and following the trail of the pigs. He carries a home made sharpened spear and is nearly naked. Descriptions of his "flared nostrils" and how he clambers on all-fours in the previous paragraph clearly suggest the idea that what we are witnessing is a regression of humanity. Being stranded on the island away from all forces of civilisation, Jack (and the other boys) is losing what defines him as a human as primitive savagery comes to rule in a dog-eat-dog world of Darwinian survival.