In chapter 8, after he stormed out of the assembly he'd called because a new vote, Ralph was still elected chief, Jack forms his own tribe. In their first meeting, he tells the boys that they are going to forget the beast. But he goes on to say that when they kill something, they will leave something for it. He believes, as he stated at the beginning of chapter 8 before he left the assembly, that the beast is a hunter, too. He believes that it could hunt and kill them if they don't leave a sacrifice for it. Shortly after he declares this at his meeting, he and his hunters kill a pig. They sharpen a stick at both ends: one end to stick into the ground and the other to stick into the head of the killed pig. This is the gift he leaves for the beast. It is this pig's head that Simon "hears" in his trance. Sacrificing to appease a power has ancient religous roots beginning before recorded time probably.
In the novel Lord of the Flies by William Golding, the marooned boys are spooked and scared by the idea there is another, dark, presence on the island as well as themselves. Gradually this idea gains shape and personality and it all comes together when Samneric run back to tell the others they have actually seen it. Jack and Roger go off to investigate too, but don't realise it is a dead pilot. The walls of reality are beginning to blur, so Jack decides to use the ancient idea of "sacrifice" or appeasement. He kills a pig and they stake its head onto a stick, hoping this will keep it happy and away from them. One of the most well-known examples of this from the Bible shows Abraham preparing to sacrifice his own son, as a sign that he will follow God's will no matter what. (In the second world war, some English politicians were accused of letting Hitler get too far by trying to appease him.)