The black group makes a comb formation with unfinished 'legs'. Here is the vital point.
Knowing the comb formation tempts one to extend the leg with . White plays to create a bulky five and plays at the vital point.
So, since the stone seemed to be the one spoiling the comb party, Black tries here. Up to he gets a ko.
here may look to be a vital point....but and ! kills, with becoming double atari.