It costs black one point. The cut is lethal: f4 pass g3... and there is no good reply left for black
so if black is first he plays f4, if white plays first she plays f4 and black has to cover the cut which cost him 1 point
(hide) If you don't want other users to know what you are doing you can change into cloak mode in Settings (paying members only). (pauloaguia) (show all tips)