Okay, he’s shown reading Joan Didion as a commemoration. But is that a separate matter from the rest of the drawing and dialogue? Or some reflection of something she wrote?
And on an almost-literal level, what is the cat reporting actually? Do mice get more dangerous as their teeth grow longer, or go soft as they age into long-in-the-tooth status? Is this about a scary encounter, or just old companions sharing whatever passes by in their minds?
Comics I Don't Understand 
That cat is simply sharing yet another amazing property of mice that appears to bother him (it’s probably just jealousy).
P.S. I’m sure the book is an unrelated tribute (she died very recently). There’s nothing obvious that suggests any connection to cats or mice, at least not in the book shown. If she revealed a rodent complex in a later work, Bliss would surely have shown that book instead.
I agree, the cat is just more interested in random mouse facts than is the man.
Pretty much all rodents have to chew to keep their teeth sharp and the right length. Not much of a great revelation.
In other news, His cat is talking to him. Real or is he having a psychotic break?
Raymond A. Levesque, it seems to me that Bliss is having his dog and cat engage in conversation (either real or through thought balloons) more and more often.
It seems to me that this tendency for pets to speak in some form more and more often affects many comics over time. Arlo seems to interact more with their cat Ludwig than I remember from much older strips. Older Gasoline Alleys never had interactions with animals IIRC, but the current version does (and there was that strange story a few months ago about Joel getting radio signals through a colander). Snoopy didn’t start out as much of a character in early Peanuts strips, but in later years became a main focus.
Have others noticed the same thing?
As zbicyclist points out, Bliss has been showing dog and cat conversing with each other, as well as with their humans. Here is today’s, where the speaker, though not clearly shown, must be a squirrel:
“If they [rodents] don’t chew, their teeth grow through their brains.”
“How very incisive!”
From “The Giant Rat of Sumatra” by the Firesign Theater
I figured the cat, chilling a bit disrespectfully near his owner’s head, was casually planting the idea that he’s vital to the safety of the household. A variation on the dog who makes a show of barking fiercely at passersby when he has an audience.
A 1/2 tin of Uncle Sigmund’s Peruvian Cocoa Powder.