The ordinary is the most wondrous, all things intra-penetrating yet just as they are ...
Dosho Port (on his blog, wild fox zen) has a wonderful rephrase of the reference to Luling rice ...
In Guishan's own teaching, one of his favorite koans was: "A hundred years from now, I will be reborn as a buffalo at the front gate of this monastery. On the side of that buffalo will be written 'Monastic Guishan such and such.' If you call it a buffalo, it's Monastic Guishan. If you call it Monastic Guishan, it's a buffalo. What will you call it?" Again, the dualities. If you call it a pitcher, you miss it. If you say it's not a pitcher, you miss it. If you call it a buffalo, you miss it. If you say it's not, you miss it. Our tendency is always to be caught on one side or the other. How do we go beyond those dualities?
calculate: for every grain of rice to be eaten, one grain must be
a single grain of rice is divided, then you will have two half-grains
Three tenths, four tenths; one half, two halves. If you supply two
of rice, you will make a single whole grain. [You must be able to see
clearly how much of a surplus will be created if you add one unit of
rice, or whether there will be enough if you take away one unit].
Getting to eat a single grain of Luling rice enables one to see the monk Guishan; getting to supply a single grain of Luling rice enables one to see the water buffalo [that Guishan will become]. The water buffalo eats the monk Guishan, and the monk Guishan feeds the buffalo. Is my measurement complete or not? Is your calculation complete or not? If you carefully inspect and exhaustively check [these matters], your understanding will dawn and become clear. Then, [when you understand these details be prepared to explain them to others according to their capacity to understand. Use ingenuity in your practice; see the buffalo and Guishan as one, not as two, even though temporarily they appear that way. In your day-to-day life, do not forget this even for a moment].
From: Tenzo Kyokun - Instructions for the Cook by Eihei Dogen - Translated by Griffith Foulk [with portion from Uchiyama]