All players must agree to allow nel-o bidding before the game begins. Sometimes nel-o is only allowed by the dealer, if the first three players all passed. A player may choose to bid nel-o, 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 nel-o bidder into catching a trick. The nel-o bidder's team scores a mark if they catch no tricks. If the nel-o bidder catches even one trick, the hand is immediately over, and the opposing team scores a mark. Other variations of nel-o 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. Nel-o rules may also be used in the domino game "Shoot the Moon." Splash The bidder bids three marks, and their partner controls the game as if the partner won the bid, without discussion with the bidder. The bidder must have three doubles to do this. Some variants have a "Splash" worth two marks. Plunge Also called Crash, this variation is exactly like Splash, except four (or in some variants, three) marks are bid and the bidder must have four doubles. Jump bids are allowed for Splash and Plunge. All tricks must be won for a successful plunge bid. If the opponents win even one trick the plunge bid fails and the opponents get the marks. Sevens Another less common rule is to allow a player to bid Sevens. Instead of the highest domino winning each trick, the domino whose sum is closest to seven wins. Dominoes are classified as "sevens" (the 4-3, 5-2, and 6-1), "one away" (dominoes adding to six or eight), "two away" (adding to five or nine), etc. When more than one domino of the same distance from seven is played, the first domino played is considered the winner. A player must bid at least 42 (one mark) to go in