We mark cells with a flag to mark them as mines and so to avoid clicking on them with the left key. The game is over if we accidentally click with the left mouse key on a cell that has a mine.

Reveal Mines\n\n With your cursor inside the minesweeper window type "XYZZY" then press Shift-Enter and Enter. A white dot should appear in the upper-left corner of the screen. If it turns black, your cursor is resting on a mine. Note: This trick works best if your Windows background is black.