(It's 100% the latter. As evidenced by the next two rounds, which end in them all throwing paper as well. Technically they could also throw rock, but none of them could throw scissors, meaning rock always lost.)

Zetta let out a low sigh. "Yes, I was a book, and yes, the Prinnies are among my cadre of loyal minions. Unfortunately, they have a little bit more self-will than the others."

Having apparently failed to resolve their dispute with more conventional means, the Prinnies broke out the Hungry Hungry Hippos, settling around the board as they dropped the balls into the center.