This one shows us, again, that Charlie Brown is probably not Snoopy's owner yet, but that
someone owns him, or where else would he have gotten that doghouse? The expectation that his yard should be mown expands Snoopy's personality further; in the middle-era, when his doghouse burned down, it would be revealed that he lost a pool table and a Van Gogh in the fire.
The dial of a rotary phone is also visible here, which things, as I mentioned before, are now receding into memory.