Some of Nibbles' off-kilterness might be because she's a hamster, specifically, the golden hamster. This species of hamster doesn't really like to be handled (they're more like "watch pets" and handling them too much can stress 'em out), they have been known to be aggressive towards any cagemates (i.e, her mate), are solitary by nature, and a lot of your hamsters that become pets didn't come from lines that were bred for more than just "cute". With all considered, she's a deconstruction of the Artistic License – Animal Care trope, a trope that would apply more pets like her.
Given all the other animals can talk perfectly well, one will probably wonder what the deal with Tchotchke status as The Voiceless is. Well, in real life, many slow lorises that end up as pets were illegally trafficked to the States. During this process, as Slow Loris' can deliver a venom that's activated with their saliva, the traffickers will use pliers to literally rip their teeth out of their mouth. Tchotchke maybe be unable to talk because someone actually removed their teeth (and, if they could talk without them, they might be traumatically mute). Worth noting is that Tchotchke hold their umbrella with their arms up, something that lorises do to better reach their venom glands.
Chico is revealed early on to be pregnant. When this is revealed, Chico flashes back to being visited by another cat, and asking if they want to "do that thing again?" If we assume from this remark that Chico doesn't really know what mating entails, it casts some dark implications on how consensual those activities were.
Amigo's cage is shown to be absolutely full of dog skeletons and the cones they wore, proving he's done the cone scam countless times before Honey came along. That's horrible as-is, but Amigo isn't some wild animal hunting to survive...he's a zoo animal who gets fed by humans on the daily. He might not even be eating the things...he's killing dogs just for fun!
Or, alternatively, his zoo diet is so insufficient that he's doing surplus kills.
Ruby's / Cherry's rant to Honey about how hard of a life she's had in the past is basically dismissed as "a lot of dogs live that way". While it could very well be an exaggeration of her puppyhood, it is told in rather blank terms (having to stay in a cage away from her mother and littermates, eating whatever scraps she got off the floor, etc.), making it all the easier to whip up the possibility that Ruby / Cherry could've come from a neglectful owner at best, or be from a puppy mill at worst.
In one episode, Diablo reveals that he doesn't have upper teeth. Y'all remember how in an earlier ep, he mentioned that he bit a kid?
