The reference in chapter 12 to the "stick sharpened at both ends" comes from the hushed conversation Ralph has with Samneric when Ralph is hiding from Jack and all the other boys. Ralph is being hunted, just like a pig, and he is a tribe of one with all the others on Jack's side now, either by choice or by coersion. Samneric tell Ralph that Roger sharpened a stick at both ends because Roger means to put one sharpened end into the ground and put Ralph's severed head on the other sharpened end of the stick. Ralph would be regarded in the same way the boys regarded the pig whose head they earlier stuck on a stick that was sharpened at both ends. That particular pig was treated that way as a sacrifice to the fictional "beast" that the boys in Jack's group feared. That head became the Lord of the Flies that Simon, and later in chapter 12, seemingly spoke and identified the real evil on the island as the savagery inside each person. By reducing Ralph to nothing more than a pig, the boys have reached complete savagery.