Naturally a discovered check can occur horizontally along a rank as well as vertically along a file. Here are a few examples of what the horizontal patterns look like. In the diagram on the left White has the makings of a horizontal discovered check on the eighth rank. The Black king is in place; the only question is what the bishop should do to take advantage of the check that will occur once it moves out of the rook’s way. It could take Black’s knight, of course, with Be7+, but it would be a mistake to settle for so little. Consider first the king’s response to the discovered check; ask whether the unmasking piece might add to a mating net. In this case the king would be forced to move to g7. Can White’s bishop attack that square when it unmasks the rook? Yes: 1. Bf6# is mate.