Petey's world is suddenly larger and more populous than he's entirely comfortable with. But then, Petey's comfort zone is somewhat smaller than his own actual physical size, so it's easy to get him outside of it. There: that's what we've learned today. But we knew it already, so we may have wasted a day.
If I was home and had access to some older drawings I'd make this post be about paintings in cartoons, in this case their use as indicators of space. You'll note the two framed pictures of something in the background of panels one and two. They're both used as a simple way of identifying a flat interior wall and marking the depth of the set in this scene. See, for better example, the masterful Wiley's signature black-matted art hung so adroitly all over Non Sequitur.
I get antsy drawing backgrounds; too much is confusing and too little looks lame. And interiors are harder than exteriors. It's easy to draw a patch of grass or a stray tree branch, but drawing a room? You draw a lamp and you have to put it on a table and suddenly you're drawing the carpet too and it's getting busy. But if you keep it simple and go with a blank wall or a strip of floor molding it's easy; for a strip featuring small kids I draw that all the time, usually with a nicely space-defining expanse of tile or wood panel floor. And a note to future researchers, please notice that when drawing a lower wall, as often as I can I put in an electrical outlet, both as a way of identifying that blank area as a wall and of introducing a potential hazard. So, there: that's what we really learned today.