Note - This is one of my favorite koans.
When the nun Chiyono studied Zen under Bukko of Engaku she was unable to attain the fruits of meditation for a long time.
At last one moonlit night she was carrying water in an old pail bound with bamboo. The bamboo broke and the bottom fell out of the pail, and at that moment Chiyono was set free!
In commemoration, she wrote a poem:
In this way and that I tried to save the old pail
Since the bamboo strip was weakening and about
Until at last the bottom fell out.
No more water in the pail!
No more moon in the water!