To explain the concept of "irreducible complexity" to the layman, Michael Behe offered the example of the common spring mousetrap. Remove any one part of the mousetrap and it fails to catch mice. Therefore, like complex life processes Behe reasoned, it could not have developed gradually from component parts, but conceived and created as a working whole. It seemed impossible to him that the mousetrap could work with fewer parts, therefore it must be impossible. Personal Incredulity = Irreducible Complexity.
It didn't seem impossible, however, to University of Delaware Professor John MacDonald. On his personal website, he presents a clever and illuminating demonstration of how the complexity of a mousetrap can be reduced and still function to catch mice.