As Ragman has already explained, 'the sound of one hand clapping' is a
ko-an, a Zen Buddhist mind exercise largely designed to show that spoken (or written) language is inadequate in describing ultimate reality (something that Fresco seems to have trouble understanding).
Here's a ko-an to explain it. There was a Zen master who always spoke to his acolytes in parables, allegories and metaphors, never giving a straight answer to a direct question. (Kind of like Jesus with
his parables
) One day one of his students asked the master to explain why he did this. The master thought for a moment, then asked, "Who of you knows what a rose smells like?"
All hands went up.
"Describe it to me," said the master.