The mock killing in Lord of the Flies demonstrates the force of the instinct that humans have toward savagery and it acts as a prelude to more acts of violence by the regressing boys. Certainly, it foreshadows the death of Simon.
In Chapter 7 the boys climb the mountain in search of the "beast"; ironically, this beast for which they search actually resides within them. When a wild boar passes through the underbrush, Ralph is able to strike it on its snout. Thrilled that he has dealt it a blow, Ralph shouts, "I hit him! The spear stuck in--" He changes his mind about hunting, too, feeling that "hunting was good after all." Clearly, Ralph has been seduced by the savage instinct within him to kill. But Jack scolds him for not waiting until he could really hurt the animal, and Jack shows Ralph how he was hurt as the fleeing boar caught his arm on his tusks.
With Ralph's moment of glory lost, with their adrenaline still rushing, gather around Robert and hold him down. Ralph, "carried away by a sudden thick excitement," grabs Eric's spear and jabs at Robert. Others shout "Kill him!" Terrified, Robert screams, but the savage Roger "fights to get closer." Finally they stop, "panting, listening to Robert's frightened snivels." Rubbing his behind, Robert suggests the others get a real pig "because you've got to kill him." This action against Robert clearly acts as foreshadowing.
Further, as the boys continue to climb the mountain, Ralph is pursued by the sadistic Roger, who bangs his wooden stick, not unlike the one with which Ralph struck the boar, against things behind Ralph in a threatening manner. Finally, the boys discover "the ruin of a face." All these actions demonstrate how the savage instincts are becoming dominant in the boys and they foreshadow further savagery, as well.