From David K. Jordan’s “Taiwanese Poe Divination:”
In temples and occasionally at home, Taiwanese routinely perform simple divination by means of two half-moon-shaped wooden or bamboo blocks, each of which is flat on one side and rounded on the other. Held with the flat sides together, the pair looks rather like a small banana cut in half lengthwise. They are inevitably painted red, and in Taiwanese Hokkien they are called poe (pronounced “bwey,” to rhyme with English “whey”).
In characters, poe is written differently depending partly upon whether the blocks are thought of as being made of wood or bamboo. In Northern Mandarin they are called jiào or jiǎo, and in Southern Mandarin bēi, all written with a variety of characters (筶, 筊; 盃; 杯).
The poe are used by throwing them on the floor to see whether they land rounded-side-up or flat-side-up. We may envision the process as comparable to throwing a pair of coins. The most usual procedure is for the petitioner to pose a question, and then phrase an answer. He then throws a pair of poe to receive confirmation or disconfirmation of the answer. If the two poe fall identically (both flat-side-up or both rounded-side-up), then the formulation of the answer is disconfirmed and a new answer must be proposed. If they fall differently (one flat-side-up, the other rounded-side-up), this represents a positive response. […]
The formulation normally requires a run of three positive responses in a row. Thus if a petitioner formulates his revelation, throws a pair of poe, and gets a negative response, he reformulates the revelation and tries again. If he gets a positive response, then he throws the poe a second time. If he gets a second positive response, he throws them a third time. The third positive response concludes the divination session on that question, since the formulation now gains the status of a confirmed revelation.