When it is your turn, you place one of your dominoes on one end of the chain and, if you cannot do so, then you have to pass, taking one domino from the pool if it is not empty. Divide the total on the ends by 5 or 3 and add the answer to the player's score. You also score 10 points for being the first to finish, plus one point for every domino held by another player, but you might not be the winner even if you do finish first. In the following example the double 5 starts, scoring 2 points. You can work the answer out mentally and then check with the actual dominoes.
People are unlikely to notice that one is missing.
Ask a friend to make the usual chain and when he has put down three or four dominoes tell him the numbers that he will get at the ends when he has completed the chain. This is a challenge that you might like to take on by yourself or with a group of friends. In this diagram the four dominoes make a 'window' with one empty space. The spots on each side total nine. One window need not have the same spot-sum as another.