The placement that kills the edge
Endgame tesuji are small moves with teeth. First, the placement. White's edge group has a straight three-space eye along the first line — alive-looking, but a straight three is dead if you strike its centre first. The placement sits inside the eye space: one stone, deep, hopeless-looking — yet after it, no single White move anywhere makes two eyes. Play it before the boundary closes; the whole group's points swing to you.