"How much is that doggy in the window, the one with the waggly tail...?" Familiar words to an old tune suggests that many people at one time or another consider having a dog as a pet.
They might have fond memories of the old Boxer or Cairn terrier that they grew up with. Maybe it was a good-natured mutt or even a neighbour's well-behaved German Shepherd. Some folks imagine owning a beautiful and heroic dog such as "Lassie" of book and screen fame.