The Amazing Domino Count Trick

Arrange twenty dominoes facedown in a row, pretending that you are doing so at random, but making sure you place the tiles in a sequence, starting on your left, with a tile bearing twelve pips, the next with eleven, then ten pips, and so on until you reach the double-blank.  The pip totals on the remaining seven tiles are irrelevant. 

You now ask your subject to move no more than twelve tiles from the right side of the row, moving them to the left side of the row, while you are out of the room.  Once you return you announce you can magically tell how many were moved.  You do this by placing your finger on the 13th tile from the left (or 8th from the right) and asking your subject how many were moved.  Once they have said the number you turn the tile over and, voila, it bears the correct corresponding number of pips.

You can further amaze your subject some more by magically naming the pip total on another tile and then subsequently turning it over to be proved correct.  Simply count off by one, two or three from the initially turned over 13th tile.  For example if it was a 5 then two tiles left will be 7.  When naming the pip totals you are announcing use "double-six" for 12 and "double-blank" for 0 to help disguise the secret method.  You may not know the different suits on each end of the other dominoes.

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