There is Death in the Hane
This proverb, "There is death in the hane", refers to the fact that the hane on the first line is a very common method of killing groups. The main purpose of the hane is to reduce the space for making eyes.
This Black group (an L+1-group) can be killed with the hanes at and . If Black blocks at a, Black's interior space is a dead bulky five. White can then kill Black with a placement tesuji at b. If Black tries playing b instead, then white will play a.
Notice that in the above examples, the hane stone is not defended when put into atari. Instead another hane or a placement follows. That is because capturing the hane stone will result in a false eye, and White can easily prevent Black from escaping to the outside (see preventing escape on the first line).