Naturalism
The movie is cited by many legendary Disney animators, including Walt Disney himself, to be the first Disney movie (and so far only) to have a suggested "sex scene." This is when the title characters wake up in the morning, cuddled together in the park, and leaving a knowledgable viewer fully aware of what they were doing the previous night. Furthermore, since they were not "married," this means the film managed to show sex out of marriage positively (albeit with consequences) which was prohibited in the Hollywood production code. This is further complicated by the fact that Lady apparently comes home pregnant, and the dogs next door are aware of it as well, whispering about the courtesy of proposing marriage to her. This gives further meaning to the junkyard dogs who chase Lady through the alley as well, which suggests she is in heat. These gentle suggestions were possible in the 1950's only because the characters in question are dogs. The next scene has Jock and Trusty proposing marriage to Lady to explain the scene to children.
Hahaha! I must confess I was completely naive about the whole thing. I don't know if it is because I still watch it through the childlike eyes that I first saw the movie, or maybe because I'm not used to such subtlety...but either way, I never put two and two together. I thought Jock and Trusty were proposing because they saw how sad and lonely she was! And the scene with dogs chasing Lady has always confused me -- I mean why where they chasing her? If if was territorial (which is what I assumed) then they wouldn't be working together. And is she was in heat (which occurred to me later) again, they wouldn't be working together.I am just amazed the Disney would put all that in! And if he did, wouldn't Lady be called something other than "Lady?"