Carl Sandburg's poem "Fog" compares the whimsical movement of fog to that of a cat. Just as a cat moves along with footsteps that are silent and skillful, creeping along without giving any signs of its movement to the ear, so does fog move quietly and inexorably, arriving without any sort of warning but also with total coverage, keeping a whole neighborhood or city under its wraps.
As the poem moves into its second stanza, the analogy of the fog and cat continues. The fog has settled in over the city, taking its new locale in just like a cat does when it reaches its new destination. Just as a cat relaxes to take in the vista, whether wild or domesticated, from a higher point, fog does as well. A cougar looks down on its surroundings from a cliff or ledge, just as the house cat climbs up on its carpeted "tree" to gaze down on its domain. The cat acts as though it is the owner of the establishment, haughtily refusing to take on the groveling role of, say, the dog. A fog possesses a similar level of mystery, eluding those who would contain it or even explain it. Both the fog and cats remain subtle mysteries.