“It’s hard to know where to begin …” Actually, it’s easy to know where to begin: What species are being shown here? But then the not-understanding bifurcates into two paths.
If the equal overall sizes, and equal tail lengths, and similar footpad design, and similar whisker attachment, together mean they are the same kind of creature — which would have to be mice? — then is there a joke besides the domestic tradition of one family member nodding off upright in front of the tv, and the fillip of the disguising glasses?
But if the white belly pattern, and rounder head, mean that’s a cat on the left — despite the muse being the same size — does the mouse’s remark amount to a comment on why there is no cat-and-mouse fighting going on?
Comics I Don't Understand 
While I do agree that the one on the right does have something “mouse-like” about its appearance, I think this is just an accident that occurred because of the open mouth. I’m sure that Ms. Scrivan intended both of them to be cats (for instance, most cartoon mice have round ears); and the domestic meme is all that is going on here.
P.S. Dark glasses are one method, but ping-pong balls are another possibility:
The tails definitely look more cat-like to me. I still don’t know what the joke is, though.
I think it would have been funnier if the mouse said, “I know you’re NOT sleeping.” Assuming the cat was getting ready to attack the mouse, but was pretending to innocently sleep.
https://www.gocomics.com/foxtrotclassics/2023/03/10
Why is it more annoying?
@ Tim H. – I’m not going to embed the image of that classic Foxtrot here, because it belongs in a separate thread of its own (it has nothing to do with the animals on the couch at the top of this post). The best thing to do would be to use the “Suggest a CIDU” form to submit that URL to the CIDU Editors.
I grew up with cats. Everything about that drawing is cat, and only cat. There is not a single mouse detail (apart from the color) on that character.
That said, I also thought it was a mouse. ——- (There must be some brain-fooling thing going on in that panel.)
Cat whiskers are below the nose; mice whiskers are above the nose.
Cat’s have triangle nose pads; mice don’t.
Cats have full padded feet ; mice have skinny little fingers and walk on their toenails.
Cats ears can be triangular; mice don’t have that feature (the shape of the mouse ear is such that a photograph taken from the side can make the ear look pointy)
Kevin, so are you saying the gray one on the right is a cat? They’re both cats?
Then it’s just the family-life patterns joke?
Though the scratch markings on the couch do support the idea that this is a feline household!
@ Mitch – I agree with Kevin: they are both cats (see @1). The eye mistakenly parses the shape above the gray cat’s open mouth and concludes that it is a long “rodent” head.
@Mitch4 – yes, 2 cats.
@Kilby – Thanks; even though I wrote that the panel was tricking me, I spent so much time on cat-mouse differences that I didn’t go back and look. In fact, my brain had been asking me earlier, why are they drawn so different?
I thought the one on the right was a dog, not that that makes the joke any better.
And it’s Becky for inclusivity!
So, having established it’s cats all the way down, the question must be asked:
WHY, and in what cat universe, would taking a nap be seen as a thing to hide?? I mean, maybe the reverse, fake sleepy eyes, and the other cat accusingly, “I know you’re not napping!”
I read somewhere a comparison between humans and cat, both the apex predator, easily fulfill their food requirements and thus have lots of free time: humans used the extra time to develop civilization, culture, traffic, pollution, congestion, all those good things; cats used the extra time to take longer and better naps. In the end, who made better use and wiser use of their extra free time?
larK, I feel very lucky that when I’m in need of a cat nap, I can usually recruit a cat or two to help me with that.
Sort of – “While the cat’s away (sleeping), the mouse will play?