... not the least of which is looking at how a middle class couple lives in 1921.
The "rarebit fiend" is the husband who has eaten a Welsh rarebit - which is nothing more than cheese toast - and has a wild dream because of it.
In the dream, "the pet" wanders up to the couple's house, looking tired and hungry. The big hearted wife takes it in. It resembles a dog, but has blank eyes so you really see no expression of menace in its face. However, feeding it makes it grow, until it eventually attains a tremendous size and threatens the city. Planes and a zeppelin are dispatched to bring it down. It does sound a bit like King Kong in the end, doesn't it?
There is a great deal of detail in the drawings, so we can see that an urban couple in 1921 has an electric toaster (the pet eats it), and there are outdoor connections to running water and hoses attached. There is a great deal of detail shown in buildings and furnishings to the point where they look like photographs in some cases.
I found it odd that at one point , before the pet becomes completely outsized, that the husband goes to a pharmacy. He calls the pharmacist "Doc" and asks for an entire barrel of rat poison which is labeled "Rough On Rats". Doing something like that today would get you labeled a terrorist, and you would walk away with no rat poison. So you could buy rat poison in 1921, but it was illegal to be sold alcohol. Oh well, all times have their ridiculous situations.
This is a very interesting animation before Walt ever got involved in the business.