It is the i-Ching (book of changes). There are a couple of ways to cast it…one way involves coins, another a pile of sticks. These determine what two trigrams make up a hexagram, which you can then look up in a book and read the meaning and interpret it.

Oh wow…I never heard Dewey say mace. Are you sure it was mace? That doesn't sound like something Cooper would do, and I agree it would have been a sucker punch.