The speaker is startled by a simple fact: every breed of dog, however fluffy or fussy, descends from the wolf. He starts with light, almost comic details, like the Pomeranian's ears and the spaniel's skirts, but then the poem darkens. He reminds us what the wolf was: glowing red eyes, huge leaps, howls in the Arctic, hunger, and teeth that tear flesh from bone.
The second half turns this wildness into a list of things wolves never did. No wolf got ulcers from sheepdog trials, ate itself sick on canned meat, chased sticks, or waited for Christmas as a little girl's wish. The humour is dry and gentle, but there's a sad edge too. The speaker seems amazed, and a little mournful, at how much has been lost or bent into service and cuteness. The final image, a dog cocking its ear at "His Master's Voice," sums up that change: a wild hunter now listening for orders. The mood is playful on the surface, with something uneasy underneath.