There are 2 serious books out right now about a man trying to live like a particular nonhuman animal.

These are nonfiction books, and they are being taken seriously. I read about them in Joshua Rothman's article in The New Yorker, "The Metamorphosis/What is it like to be an animal?"

Two men — Thomas Thwaites and Charles Foster — independently conceived of their projects. Thwaites, an artist, tried to be a goat and wrote about it in "GoatMan: How I Took a Holiday from Being Human," and Foster, a veterinarian/lawyer/columnist, tried to be a fox and a badger and wrote about it in "Being a Beast."

These projects were entirely different from fictional efforts at inhabiting the existence of a nonhuman animal, such as Tolstoy's "Strider" (about a horse) and James Joyce's "Ulysses" (with a bit about a rat). As Rothman sums those up:

In these pastoral and sensual portrayals of the animal self, different critiques of the human self are embedded. For Tolstoy, the problem with people is that they’re marooned in their egos. The clearheaded directness of animals is a remedy for that self-obsession. For Joyce, the problem is that people are sleepy, numb, and incurious. We could learn, he thinks, from animals’ eager sensuality. Tolstoy’s animals teach us to be good; Joyce’s teach us to be alive.

What Thwaites and Foster were doing was different from that: They were using the animal not to understand humanity but as an escape from something they already believed about human beings. Thwaites finds "human personhood... stressful, absurd, and—worst of all—narcissistic" and wants to lose his ego. Foster finds human personhood dull and seeks a more vivid existence.

Rothman ends his essay like this:

There is an irony to these books: the more Thwaites and Foster try to change into animals, the more fully they become Thwaites and Foster. That’s not to say they never transform themselves... “Real, lasting change is possible,” Foster writes, “to our appetites, our fears, and our views,” and despite that change the self persists. This ability to endure through change is the miracle and mystery of selfhood. Rethinking who we are; dreaming up new ways of living; taking ourselves apart to build ourselves back up—for human beings, these activities are natural. They are our never-ending hunt.

That is, thinking beyond what is natural and trying being what you are not is even more human than continuing your conventional ways. A nonhuman animal would never even think of such a project, let alone attempt to execute it. And, that's why these projects are, on their own terms, incoherent. You're never less like a nonhuman animal than when you are trying to be a nonhuman animal. Only a human being would do such a thing.