I've actually already started. It's a book about atheism and religious belief, and the working title is Divine Epilepsy.
This references a wonderful quote that I encountered a few months ago:
"Men think epilepsy divine, merely because they do not understand it. We will one day understand what causes it, and then cease to call it divine. And so it is with everything in the universe."
– Hippocrates, Greek physician and the founder of modern Medicine, circa 400 B.C.