One player represents the Cats, the other, the Dogs. The board starts off empty and the two players take turns to place one of their pieces on an empty space on the board. Cats and Dogs are natural enemies and may not be placed next to one another, i.e. the may not be placed in adjacent squares that share the same edge. Diagonally adjacent is fine.
 
In the regular game, the first play who can not make a move loses; in the losing game he wins.