The boys' first kill during a hunt in chapter 4, most aptly symbolizes their loss of innocence. They had killed a live thing and had seen its blood. Instead of being horrified at the blood and the animals' death, they were exhilarated and proud of their success. In fact, they had created a terrible chant to indicate just how much they had been corrupted by their deed.
“Kill the pig. Cut her throat. Spill her blood.”
The horribly graphic nature of the chant is further emphasis of the depth of their loss. Where, before, they would probably have been horrified by the idea of killing something, wilfully cutting its throat and spilling its blood, they now celebrate it. These are boys from a civilized society where the public slaughter of animals has become a thing of the past yet, in their minds, they have done something good. Killing has become something to be proud of.
The boys are so overwhelmed by what they have done that each of them has to express his role in the slaughter of the pig.
“Look! We’ve killed a pig—we stole up on them—we got in a circle”
Voices broke in from the hunters.
“We got in a circle—”
“We crept up—”
“The pig squealed—”
The fact that the fire has gone out and a possible rescue has been missed, is seen as an irrelevant detail and is dismissed with disdain. The boys, instead, continue providing details of the pigs's slaughter and relish talking about it. They have discovered within them an atrocity that would henceforth dominate their actions. The boys who participated in the hunt have changed irrevocably.
This much is evident when Simon is later killed and Piggy is murdered. It is accentuated later when they hunt Ralph with the deliberate purpose of wanting to kill him.
Ralph's participation in a hunt in chapter 7 symbolizes his loss of innocence.
Ralph found he was able to measure the distance coldly and take aim. With the boar only five yards away, he flung the foolish wooden stick that he carried, saw it hit the great snout and hang there for a moment.
...Ralph was full of fright and apprehension and pride. “I hit him! The spear stuck in—”
He is overwhelmed by having actually deliberately hurt a live animal and is in awe of the experience, so much so, that he later becomes an active participant in the hunt game when Robert plays the boar and the others attack him.
Ralph too was fighting to get near, to get a handful of that brown, vulnerable flesh. The desire to squeeze and hurt was over-mastering.