Fourth possible move;

The black pawn at F7 attempts to move down two tiles, proclaiming he is executing an en passant maneuver.

This causes the very old chess board, which has seen quite a lot of chess games and hates nothing more than the misunderstanding of the en passant maneuver, to open up its great maw, declare that the pawn has 'activated his trap card', swallow the pawn into sheol/hades underneath the board, and from there belch forth the mighty white eyes blue dragon, which takes up 2x2 in the center of the grid, is allowed 3 moves per each set of a black move and a white move, and appears to be hostile toward both white and black units.