The key is the hekomi of , making a tiger shape. Notice that Black cannot play at a. And if Black plays at b, White will play at a.
If blocks, descends and secures one eye. If at , then , Black a, White b, Black c, White d, and White still secures the eye on the right side.
The interesting part comes when attempts to destroy the other eye. However, White can play as in Beginner Exercise 19, making the throw-in at and capturing three black stones in a connect-and-die to form the second eye. Subsequently, if Black a, White b plays atari.
(or a) trying to expand the eye space fails instead. The wedge at is the vital point, and is a common killing technique. Now it is not possible to make a real eye on the left side.