Four concealed matching tiles can become a kong.
A concealed kong starts with four identical tiles in your concealed hand. On your own turn, you can draw a tile from the wall, then declare the kong.
Even though it started as concealed, you must announce it and expose it in your open melds area so the table can verify it. After exposing your Kong, you need to draw a supplement tile from the dead wall to keep your total tile count at 13. You must expose a Kong for it to count as a meld.
