This occurs when a player Hu on drawing the one of marbles when there are only 5 or less tiles left in the wall.

Variations include:

(i) Hu on any tile drawn from the wall when there are only 5 or less tiles left, or

(ii) Hu on the last tile drawn from the wall.

This occurs when a player Hu on a tile that another player wishes to Kong an exposed Pong.  If Player B has Ponged and wishes to Kong with the last tile, Player A can Qiang Kang. In this case, Player B is considered to have discarded the winning tile. Player B is also not compensated for the attempted Kong.

Note that it is not possible to rob an Um Kong.  The only gaming hand that can steal an Um Kong is the 13 Unique Wonders / 13 Orphans hand (Shi San Yao).

This occurs when a person Hu on a tile drawn from the flower pile (after replenishing a flower/animal or topping up a kong).  

Variations include: 

(i) consecutive Hua/Kong Sang (i.e. if a person draws a flower/animal or melds a Kong, draws another flower/animal or melds another Kong from the flower pile and then Hu), then the Hua/Kong Sang Hua/Kong is worth limit), 

(ii) cumulative Hua/Kong Sang (e.g. if a person draws a flower/animal or melds a Kong, draws another flower/animal or melds a Kong from the flower pile, draws a third flower/animal or melds a Kong and then Hu, then the Hua/Kong Sang Hua/Kong is worth 3 Doubles), or

(iii) Zha Hu instead of Hu if a player wins after replenishing 3 consecutive flowers/animals/Kongs.