In the poem "Fog," the phrase "little cat feet" is a metaphor used by the poet Carl Sandburg to describe the way fog arrives. By comparing the fog to "little cat feet," Sandburg emphasizes the stealthy, quiet, and gentle nature of fog. The comparison suggests that fog moves softly and unassumingly, much like the delicate and silent steps of a cat. This metaphor helps create a vivid image of the mysterious and elusive qualities of fog as it envelops its surroundings.