The idea that the mousetrap is no use with any single one of its parts missing is examined. Creationists often use the mousetrap as an example of a machine that must have been designed as a complete machine - not evolved from a simpler machine. Of course it was designed that way! Its a machine!
This is an analogy of course, and as I explained recently, analogies are useful teaching aids but they do not really explain anything about the truth.
However, extending this particular analogy as a tool for real learning, the truth is that a mousetrap-like device has other uses.
Evolution cares little for intentions and cares a lot about opportunity. The mousetrap idea explains perfectly how seemingly impossible features arise from one useful feature which accidentally becomes useful in another way.
Hoisted by your own petard?