One point kills the flower
The flower five (梅花五) is a plus-shaped space of five points, and every arm of the flower passes through one centre point. That centre is the whole shape's single vital point: strike it and your stone touches all four arms at once, after which no amount of filling gives White two eyes. Anywhere else lands on one arm alone, White answers at the centre, and the flower rounds into life. White to play: kill Black — take the centre of the flower.