Nello
There is an optional house rule that allows players to bid "nello" (also known as nillo, nil, low, or low-boy). All players must agree to allow nello bidding before the game begins.
A player may choose to bid nello, instead of bidding a number or passing, if they have particularly low dominoes in a hand (the -blanks and -ones of several suits). This means they intend to win the hand by not catching any tricks at all. Their partner then turns their dominoes face down, and does not participate in that hand. The opposing team will play their lowest dominoes, trying to force the nello bidder into catching a trick.
The nello bidder's team scores a mark if they catch no tricks. If the nello bidder catches even one trick, the hand is immediately over, and the opposing team scores a mark.
Other variations of nello treat doubles in a special way. Doubles may be weighted either as the high of their suit, as a suit of their own, or least commonly as the low of their suit. If any of these variants are used, a declaration is required and all players must agree to allow them before play begins.
Nello rules may also be used in the domino game "Shoot the Moon."
Read more about this topic: 42 (dominoes), Optional Rules