Dashes seem to be places that might be a mine but also might not (because the game has to reserve the right to move mines around depending on where you click).

Dashes seem to be places that might be a mine but also might not (because the game has to reserve the right to move mines around depending on where you click). In this case it's telling you that 6 over (zero indexed) and 2 down (the spot is marked with an asterisk in the second diagram) is safe, because of the pattern of "ones" on the left edge.