Why does the author have roger stick a spear up the pigs butt in lord of the flies?

Well, honey, the author, William Golding, had Roger stick a spear up that poor pig's butt to symbolize the boys' descent into savagery and the loss of civilization. It's a brutal way of showing how power and violence can corrupt even the most innocent minds. So, next time you see a pig, maybe give it a little extra respect, yeah?