At the point in time when my main plot starts and the modern Feline Democratic Republic starts existing, nutritional and biochemical requirements have been (at least technologically) solved, there is something called a Dietary Enzyme Supplement that supplies your digestive tract with artificial enzymes, allowing you to digest plants (including cellulose), and even directly synthesize essential nutrients only found in meat inside the digestive tract. However, access is still an issue depending in where you live and what species you are. The Feline government provides supplements (and food in general) for free at the point of use, it’s all tax funded and entirely subsidized. That is written in their constitution because it’s one of the major things the revolution fought for. On the other side, other territories and taxa, particular the Trophist (pro-predation) governments, often outright ban plant based alternatives because they see it as a threat to their ideology (though the common excuse is that it is “unsafe”), but those places obviously not only not criminalize predation, but actively encourage it. If they were going to Feline territory they would be under the jurisdiction of the Feline government, and they would need to follow the Interspecies Peace Agreement and Feline law or face criminal sentences, but, they also have access to to those supplements and food that the Feline government guarantees.

More lore if you’re interested: The progression of plant based alternatives was not a binary “from this moment on you no longer need to eat prey!” Take Felines for example, obligate carnivore and therefore one of the most difficult taxa to develop plant based alternatives that are fully nutritionally complete. Before the breakthrough invention of dietary enzyme supplements (not just any enzymes either, the ones for Felines is the most recent and represents the absolute bleeding edge of protein science and biochemistry), they had direct nutritional supplements, similar to how we have vegan cat food today. However, they were extremely expensive as you had to replace nearly 100% of your biomass intake with these artificially synthesized supplements, and the Trophist government did not make obtaining the easy and most of the plant based products available to cats prior to the revolution was from grey-market, unregulated, under the table operations from Unitist cells operating illegally under their Trophist regime. Even when sold at cost as most of them were, the cost of production and materials was still prohibitive. But even when you had access to it, it was extremely easy for a cat, especially a kitten with much higher nutritional requirements than adults, to become dangerously malnourished with a vegan diet unless you paid extremely close attention to your food intake and balanced every essential nutrient perfectly, which is predictably almost impossible to do for nearly all of the impoverished Feline working class, but even so most were still determined to not eat prey (even back then both working relationships and friendships between cats and animals like rodents and birds were not exactly uncommon, so the vast majority of cats saw them as friends and not food) and the illegal use of nutrient supplements exploded and spread to nearly everyone, much of the frustration of the Feline empire who tried to crack down on it numerous times, war on drugs style. Their go-to excuse was that nutrient supplements were toxic and unsafe for Felines (so they’ll throw you in prison if they catch you taking it because that’s how much they cared about the “health” of their cats).

My main character is a cat who was actually involved with the production of nutrient supplements, develop of a Feline dietary enzyme supplement, and the revolution. The development of an enzyme supplement that is fully nutritionally complete for Felines, which allowed them to directly digest plant based food, was actually what sparked the Feline revolution and civil war. The imperial government tried to ban its further research and development, again stating that it was unsafe (so unsafe that chemists are not even allowed to research it), but at that point the working class was just like “screw you” and decided to kill the king. This wasn’t the first time an overthrow of the empire had been attempted, but it was the time it succeeded.

The enzyme supplement for felines is the most advanced of these, called ATDP (short for the Almondtail-Dandelionpaw Formulation), after its inventors, two cats, Yvonne Dandelionpaw and Nikita Almondtail, and is a white capsule that you swallow once a week. The capsule is filled with the powdered enzymes, along with stabilizers and preservatives, and has four chambers. The outer casing dissolves in the stomach, revealing three spherical inner capsules packed in powder to fill the extra space. The first layer of powder is for the stomach. The three inner capsules all have different thicknesses of the casing, and thus will break open in the upper, mid, and lower portions of the small intestines respectively. The enzymes then literally attaches themselves to the walls of the digestive tract and starts reacting with both food and the body’s own digestive enzymes. Your body does that last part naturally by the way! They’re called brush border enzymes and attach to the walls of the gut so they aren’t wasted by getting crapped out after only one “cycle” of digestion. They are reabsorbed and recycled by the cell once they’ve become degraded from performing so many reactions. The enzyme for digesting lactose is one of these! And this is why you only need to take one pill a week instead of one with every meal. This one pill allows the body of an obligate carnivore to digest and derive nutrients from plant matter, and even synthesize essential nutrients inside their bodies. So they really have no excuse.

A) Remember that humans are animals. We may be more intelligent than others, but we’re still animals. Additionally, despite having evolved from apes, most apes have different personalities and instincts than our own. They still share many similarities with us, but gorillas, for an example, see bared teeth as a threat, while chimps view it as a sign of submission or non-hostility, and finally, humans view it differently depending on context (bared teeth can be a sign of happiness, fear, anger, etc). As such, while you might use the “primitive” personalities as a starting point, remember that they’re likely to change as the species gains intelligence and splits from their ancestors.

I definitely try to fit species specific things into their respective cultured as best as I can. For example, a slow blink and head turn in Feline culture is akin to bowing in classical East Asian cultures. In-universe, there are even “How and when to slow blink in Feline territory, Feline etiquette 101” tutorial videos for other species traveling there now that the Felines are ISPA signatories and relatively safe, because its etiquette isn’t super straightforward and they do want to make an effort to tailor their behavior to who they’re interacting with. A lip lick from a dog (a Canid in general) is common knowledge to nearly all species as a gesture of discomfort or stress in the same way it is for real dogs (which is important to know because it could also be mistaken for “I want to eat you” if you don’t know the context, as is a cat fidget-moving the tip of their tail. Another real-life parallel that I took inspiration from: in Mandarin Chinese (I think it’s the same in Cantonese but not completely sure), the word for “that” when referring to the object or subject matter of focus, and is also a very common expression whose purpose is similar to the “uhh…” that English speakers say when they’re trying to think of what to say next, sounds very similar to the n-word, and the worse one of the two at that. This is nobody’s fault, it’s just an unfortunate coincidence because those two things developed independently, but it still causes unnecessary friction when certain cultures interact and a major part of the solution is to have both cultures know the other’s context and be mindful of that. I was actually explicitly taught this by my parents as a kid, because we’re Chinese immigrants in Canada where there are also a lot of black people and people in general are a lot more familiar with that sound being a word you really shouldn’t be saying. All this is to say that I do try to take advantage of the fact that they are animals in the story, using my own life in a multicultural setting as some of my inspiration for how different animals with different, sometimes conflicting behaviors can interact amicably.

This actually takes place millions of years after humans mysteriously disappeared from the planet, so they know about humanity and our history from the ruins we left. But they also don’t judge humanity as a species for what we did in the same way we in our modern day don’t judge, for example, Ancient Mesopotamia and rail on them all the time. Animals being united hating humans felt way too clichéd so if you or I went there, as long as we abide by their laws they will totally be cool with it!

C) I can see the logic of execution going both ways, especially in the context of a predator/prey society. I could see it as being a symbol of an individual’s worthlessness, i.e. he’s so worthless we killed him and discarded his meat; not even the apex predators want to eat him.

Among most anti-predation carnivore species (former predators basically), the majority thought is “we kind of need to repent for our entire history of predation, and we’ll do that by coming down as hard as we can on cases of predation and basically ‘avenge’ the animals they killed as a way to clear our own names.” However, most of the “prey” species are against the death penalty even for carnivores because they see it as "well you’re still killing animals and even killing carnivores isn’t right, and also a slight amount of mistrust at predator species that claim to have sworn it off still engaging in killing.

As for providing food, not in this world. They don’t even allow lab grown meat despite being technologically past the point when they can make it. And yes, part of that is explicitly to not incentivize use of the death penalty.