This happens in chapter 4. Throughout this chapter, a striking difference is emerging between Jack and Ralph. Ralph wants to accomplish tasks that help make the children a successful society, and Jack grows more bloodthirsty to kill a pig. This need to kill has criven Jack to complete the symbolic ritual of face-paint, which must have aided his ability to kill a pig because this is the very act that kept the choir boys from tending to the fire.
Ralph discovered no boys next to the fire, but plenty of fuel for the fire. He then discovered that a celebration was underway of a pig that the choir boys and Jack had captured. In fact, they are actually chanting a lyric to the pig:
"Kill the pig! Cut her throat. Spill her blood."
This pursuit obviously kept the boys off track and though it may have provided temporary satisfaction, it also may have prolonged their stay on the island.