What is the significance of the chapter title "Beast from Water" in Lord of the Flies?

In the novel, a number of young boys are trying to survive on a deserted island, but suspect there is a 'beast' on the island that is dangerous and poses a threat. Each of the primary characters is an example of a part of the human mind; Piggy is the rational mind, Simon is the religious mind, Jack is the reactionary mind, and so forth. The kids meet to discus the possibility of a beast on the island. Simon and Piggy believe it is either another boy from the group or imagined fear, but Jack tries to rile the kids up with possibilities, one of which is that it is a beast from the water.
The significance of this is that Jack has brought up a possibility that is not only difficult to believe, but is not even based in fact. Either way, it does not matter; Jack is able to stir a fear of the unknown in the kids, and is able to control them without providing any real evidence at all.