When you may call
When a tile is discarded, any player may call it if it completes a group of three or more identical tiles in their hand — for example, holding two green dragons, you may call a discarded green dragon to make a pung. You expose the group face up on top of your rack and then discard.
You may call any tile, including one that completes a single or a pair, only if it gives you Mah Jongg.
Priority
If more than one player wants the same discard, a call for Mah Jongg beats a call for an exposure. If two players want it for exposures (or both for Mah Jongg), the player next in turn after the discarder wins it.
Calls should be made promptly; once the next player has drawn and racked a tile, the discard is dead.
Using jokers in exposures
Exposures may include jokers: a green-dragon pung could be two green dragons and a joker. Any player may later exchange a real green dragon for that joker on their turn. Exposing jokers therefore carries a risk; experienced players think carefully before calling with joker-heavy groups.
Concealed hands
Hands marked C on the card must be completed without exposures — you may only call a discard for the final winning tile. If your chosen hand is concealed, you will need to resist calling even very tempting discards.
