Thanks for the replies. I paraphrased the quotes from dhamma talks but will have to find them on my mp3 player. Below is some additional info that I found.
"In trying to answer the Koan, the student will come to a mental "precipice", as it were, where all the methods and procedures of accepted thinking no longer function. The purpose of the Koan is to shove the student over this precipice into an area of experience that is completely new. This is the spiritual reality that the Zen master is attempting to guide the student towards."
" What is the sound of one hand?" Of course, in terms of the conventional world there can be no sound from a single hand. Sound logically needs two hands clapping. However, the question presumes that one hand clapping has already created a sound and that it can be heard. The question is not about sound or hands clapping, although this is quite conceivable within the context of Zen. The question is rather about hearing the impossible, which is only termed impossible within the framework of conventional reality. The Zen master is therefore pressing and encouraging the student to critique ordinary reality and to force the mind into other areas of understanding."http://www.essortment.com/understanding ... 42451.html