A walk in the woods turns into a quiet comparison between living things and machines. The speaker starts with a plain fact: fungi breathe much as we do, taking in oxygen and giving off carbon dioxide. Then the poem shifts to a puffball, which becomes "an abandoned factory." The image fits well. A spent puffball is a hollow shell that has already released its spores, like a building that has stopped producing.
The speaker pokes the "intact wall" with an umbrella and finds that it's "all out of smoke." That small, almost playful gesture suggests curiosity and a gentle sense of disappointment, as if the speaker is checking whether anything is left inside.
The last stanza brings in a friend's remark about ovenbirds and the black morel, followed by "Impossible to see." The mood is light, wry and observant. The speaker is hunting for something elusive, and the poem seems to accept that much of nature stays hidden.