In this book, Pi learns about Hinduism. One major part of Hinduism is Dhabihah. Dhabihah is the act of ritualistically slaughtering an animal to eat(excluding fish) In this book, when Pi is on the raft a bunch of flying fish land on the boat. Pi picks up one of the fish to use as bait, but has a hard time killing it. I think that he knew he was going against his practices by killing the fish, which was why it was hard for him to kill it.