Insentient beings are often conceived of as comprising the physical universe—what we call “nature,” and think of as really dead, nonliving. People unwittingly or romantically anthropomorphize nature but think that nature is insentient. To put it another way, we draw a boundary between sentient and insentient, perceiving and judging each in a particular way. Dogen rejects such a conception of nature. From the standpoint of the Way, insentient beings do elucidate dharma—not in human language, but in their own expressions—hence they are alive in their own way. What Dogen is saying is that insentient beings are sentient, sentient beings are insentient—no separation. When we perceive reality in terms of the separation that begins with the boundary between self and other, we extend this perception to everything else—good and bad, up and down, heaven and earth, heads and tails, black and white. Yet every one of these dualities is two parts of the same reality—not two separate things.
From Mountain Record of Zen Talks by John Daido Loori, page 64