Symbolism runs rampant in post-world war apocalyptic cinematography, and Peter Brook's Lord of the Flies provides a baseline for the symbolism of the coming of the judgement day and the end of society. His greatest symbol gleams in the light, all curves and smooth edges, sharp points and reassuring grips. It is a confirmation of leadership, for without making a sound, it inspires awe and fear. It is a symbol, a tool, a weapon, a life-giver, and a life taker, carving out its place in society as any useful tool does. It is deadly in the hands of a child or an adult. It is a knife, and it belongs to a child who lacks its elegance and discretion. On an island of boys without an authority, they are forced to find their own. Jack, the head choir boy and only competition of 'civilized' Ralph and his noisy but otherwise useless conch shell, wields the pragmatic knife in opposition. Its uses eventually extend from simple technology, to a psychological shield for Jack, and a validation of his claim for
leadership.

Jack's knife was the only piece of 'civilized' technology on the island. It was manufactured, probably mass-produced somewhere on the mainland, and Jack puts it to its real use - hunting. First he attempts to kill a pig with it, but at that point in the film he is still too frightened of the consequences of killing, because he has alternately been taught that it is wrong to kill, but at the same time, there is a war going on and food, specifically meat, becomes necessary for survival. Thus the pig is the impetus, provided by the knife, that Jack needs to decide to survive at any cost. Technology also builds on itself, one innovation leading to another and another, constantly improving on the tools at one's disposal. Jack uses the knife to provide spears for the choir, for hunting and for defense. The spears were eventually improved upon to make stakes for the pig's head left to the Beast, and a crude rotisserie for the meat. In a savage society, having the technology means having the power.

Jack also, less noticeably, uses the knife as a psychological shield. As a child
stranded on a deserted island, with no one to assure him that everything is all right, the knife is his one connection to adults. Although he might have scavenged it from the wreak, before he boarded the plane his father or someone else he looked up to might have given it to him 'just in case' he had a run-in with the enemy, or to prove that he had some misplaced faith in Jack's maturity. At several points during the movie, Jack can be seen scoring and marking the tree at the assembly rock for no other reason than the fact that he can. It is likely that the knife was reminding him of the knife-giver, thinking 'what would he do in this situation?'

The knife, in that sense, helped establish Jack's claim to leadership of the tribe. The knife was directly opposite the symbolism provided by Ralph's conch, and even the erstwhile chief did not deny Jack's claim to leadership of the choir. It is likely that the boys were taught that knives were for adults only because they were dangerous, and the fact that Jack had one and could use it made him, in their minds, a figure of authority. That simple beginning made them susceptible to Jack's offer when the time came to split from Ralph's tribe. His inborn charisma helped, of course, but without the knife, the other boys would not have respected his authority.

Jack's use of the knife widened from it's original parameters, that of technology, to help him cope with disaster, and to help him solidify his claim to leadership. Despite the escalation of violence on the island, Jack succeeded in achieving the bare minimum of a eader's responsibility by providing protection, sustenance, and shelter to his tribe long enough for them to be rescued. If his tenure was violent and dissolute, that was the fault of the wielder, not of the knife.