Pawns have the potential to unmask attacks by other pieces in every direction; and because they are worth so little they easily can create bothersome threats, making them marvelous at unveiling discovered attacks. Pawns and pieces frequently are on the same line without it meaning much, so pawn discoveries often are less obvious than the kernel of a discovery involving two pieces—easy to overlook for you, but also for your opponent.
Pawns can only move forward (we’ll treat captures as a kind of forward movement), so the patterns they create when discovering attacks take two forms. First, they can unmask diagonal attacks by bishops and queens, and horizontal attacks by rooks and queens, as they move up the board; this makes it important to notice anytime a pawn is on the same diagonal as a friendly bishop or queen. Second, and interestingly, by making a capture and thus moving diagonally a pawn can unmask a vertical attack along a file by a rook or queen. This means you want to notice anytime you have a pawn in front of a rook or queen on the same file—not an uncommon state of affairs—and to think about whether the pawn can make a capture (or whether a capturing opportunity can be created) so that it unleashes a discovered attack.
We won’t be distinguishing very carefully in this chapter between ordinary discovered attacks and discovered checks, because discovered checks comprise such a large part of the universe of all pawn discoveries. It's very useful to have a check at one of the two ends of a discovered attack; and since pawns rarely are in a position to check the enemy king themselves, the job of giving check very often becomes a task for the other, unmasked piece.
Begin with the example to the left, where it's Black's turn to play. Perhaps the most common form of pawn discovery is this pattern: a discovered check that arises when you have a bishop or queen aimed through the middle of the board at the enemy king, and with one of your pawns blocking the way. If the pawn can move forward with a threat, the results can be crushing. Here Black has d4-d3, forcing White either to move his king and lose his queen to d3xQ, or (the better move) to sacrifice the queen by moving it to f2, allowing it to be taken there, and then recapturing with the rook.