How do I stop my iPod from playing audio books when I 'Shuffle Songs' On my main menu in my iPod, I frequently click 'Shuffle Songs' to play randomly through my songs.  It manages not to include my podcasts but every once in a while will play a chapter from an audio book.

Is there a way to stop the Audio Books from mixing in with the music?

I have an iPod nano if that matters.
In iTunes, view info on the problem audio books and ensure "skip when shuffling" is checked.