The speaker watches a dog run and wishes she could do the same. The first section is a breathless rush of verbs, "dart, leap, jump, on a tear, on a spree," and then a string of "if I had" conditions that admit she is not built for it: no floppy ears, no swooshy tail, no four legs. The humor is gentle, and the longing underneath is real. She also wants the dog's way of stopping, giving complete attention to a scent or a mole.
The second section contrasts the dog's winding path, led by its nose, with the "sedate" straight lines of human life. The dog's "intention and abandon" take turns, so wildness and focus work together rather than against each other.
The ending asks for freedom, either to be let off the leash herself or to let the dog go. The last line, "dogs run in jazz," suggests improvised, playful movement, and the mood is joyful, wistful, and a little cheeky.