A discovered check happens when you move one piece out of the way, revealing a check from a piece behind it. The moving piece is free to do almost anything — even capture or attack elsewhere — because the opponent must first answer the check. This makes discovered checks very powerful. The strongest version is double check, where both the moving piece and the revealed piece give check at once; the only legal reply is to move the king, since no single block or capture can stop two checks. Set these up by lining a rook, bishop, or queen against the enemy king.