This shows savagery because they are using a completely different source for what they are trying to do. Instead of using some type of matches, they are using Piggy's glasses.
Jack represents savagery
Their masks represent the two different personalities they have, savage and civil.
""Kill the pig! Cut his throat! Kill the pig! Bash him in!"" This quote describes how Jack has changed and how his savagery starts to show as there is no one to tell him right from wrong.
"I painted my face--I stole up. Now you eat--all of you--and I--" This quote describes how the boys are becoming savage because if they were living in the real world they would have never painted there faces and they wouldn't be talking how they are.