Guessing stone
In Zendo the Master gives these stones to students who guess correctly during a Mondo. At the end of your turn, you can redeem guessing stones with the Master in return for opportunities to guess at the Master's secret rule.
![](http://static.miraheze.org/looneypyramidswiki/thumb/e/e8/Stones.jpg/240px-Stones.jpg)
In the official Zendo set from Looney Labs, these stones are green, though any color other than the two colors used for marking stones is fine.