“Kill the pig. Cut her throat. Spill her blood.”
Immediately after their first successful hunt, Jack’s hunters chant as a group, showing that they prefer to enact violence as a mob, rather than as individuals. Their chanting shows their cohesion, and their delight over killing becomes ritualistic.
“Simon was crying out something about a dead man on a hill… The sticks fell and the mouth of the new circle crunched and screamed. The beast was on its knees in the center, its arms folded over its face. It was crying out against the abominable noise, something about a body on the hill… At once the crowd surged after it, poured down the rock, leapt on to the beast, screamed, struck, bit, tore.”
This quote suggests otherwise moral beings will subject themselves to immorality for the purpose of joining a group. When Simon is murdered, the boys think that he is the beast, and enable each other to believe this fantasy. Again, they kill as a mob, nobody stepping in to disrupt the collective fantasy or prevent injustice.
“There had grown up tacitly among the biguns the opinion that Piggy was an outsider, not only by accent, which did not matter, but by fat, and ass-mar, and specs, and a certain disinclination for manual labor.”
If most of the boys are vulnerable to the attractions of being part of a group, Piggy is firmly independent. His lack of physical prowess and his tendency toward thoughtfulness make him a bad fit for mob mentality. His virtues–wisdom, patience, goodness–are not immediately apparent or attractive to the rest of the boys.
“Memory of the dance that none of them had attended shook all four boys convulsively.”
After Simon is killed, Piggy, Samneric, and Ralph, all struggle with what they saw. Only Ralph is able to correctly remember it as murder. The other boys pretend they didn’t see it, or that they weren’t there, or that it was an accident. This kind of willful ignorance and delusion enables mobs to behave brutally or immorally.
“… the mask was a thing on its own, behind which Jack hid, liberated from shame and self-consciousness.”
In order for the boys to commit violence, they need to subjugate their individual morality, and senses of shame to the will of the group. Golding reflects the psychology of mob mentality here, showing that Jack uses his facepaint to silence the good in him, and enable him to be ruthless and shameless.