Of all confrontations between man and beast, there are few as unforgiving as the encounter between a moose and a motorized vehicle. Picture it: A stubborn, cranky and frankly enormous creature wanders out of the forest for which it has been exquisitely adapted since the early Pleistocene and into a distinctly new environment, a road, along which a car-bound human is hurtling at a speed surpassing that of any other North American land mammal. The run-in is unlikely to end happily for cervid or hominid.

In 1986, a group of Swedish bioengineering students carried out an experimental collision with a living moose with the aim of developing a “moose crash test dummy,” Mary Roach writes in her book “Fuzz: When Nature Breaks the Law.” As there is no good way to truss up a pre-euthanized moose for simulated impact, the students put an ailing moose to death and then immediately hit it with a car — specifically a Volvo 240, since “apparently the Volvo 240 is a car that goes from 0 to 50 quickly enough to reach a moose in the fleeting moments between its death and the crumpling of its legs.”

Details like these keep “Fuzz” moving breezily through a selection of ongoing conflicts between humans and the species that happen to get in our way. “Of course, these are not literal criminal acts,” Roach writes, since “animals don’t follow laws, they follow instincts.” These natural urges bring certain animals (and plants!) into friction with human systems, with consequences ranging from the deadly to the merely annoying. In all cases, these are “simply animals doing what animals do: feeding, sh---ing, setting up a home, defending themselves or their young. They just happen to be doing these things to, or on, a human, or that human’s home or crops.”

The result is a quixotic and somewhat meandering journey of a book, but one powerfully propelled by the force of Roach’s unflinching fascination with the weird, the gross and the downright improbable. Some nonfiction writers like to blend into the background, like game hunters in a blind, waiting for their subjects to produce the perfect quote; Roach is just as likely to stumble into the frame to deliver one of her own. For instance, when informed that the weapons on display at the “gun library” of a Nevada Cabela’s store are not for borrowing, she quips on-camera, “Then it’s not much of a library, is it?”

There’s a wacky genius to these interjections, frequently made at her own expense and often amid some particularly gory set-dressing. Watching a simulated autopsy on a manikin representing a bear-mauling victim, Roach notices “two small divets along the spine,” she writes. “I hazard a guess . . . that a small woodland creature might have been gnawing on our corpse.” The instructor informs her that “those are marks from the injection molding.” Roach sheepishly explains, “Part of the manufacturing process of the manikin, he means.” On another occasion, she interrupts her own reporting to confess that she has been distracted by celebrity name-dropping at a nearby table, and then duly interpolates Reese Witherspoon and Miley Cyrus into the discussion of predator populations. The effect is one of hapless relatability: author as bumbling travel companion, or as court jester, expertly capering to disguise her expertise.

This keen eye for quirk runs through Roach’s career — that, and a penchant for catchy, single-word titles: “Bonk,” “Gulp,” “Stiff,” “Spook” (2010’s “Packing for Mars” being a garrulous exception). Like haiku, these monosyllabic titles are dense with meaning, and “Fuzz” follows the pattern in evoking both the furry elements and their attempted enforcement. Below the clever surface of her prose runs a preoccupation with human occupations. You can see it in her attention to business cards and job titles, which she collects like a philatelist raiding a flea market: Human-Elephant Conflict Specialist, Bear Manager, Danger-Tree Faller-Blaster. Institutions, with their many bureaucratic branchings, provide an especially rich selection of ecological niches in which to uncover highly specialized forms of life. In “Grunt,” her 2016 book on “the curious science of humans at war,” Roach interviewed U.S. Army fashion advisers and stink-bomb engineers, delighting in discoveries such as a Hook and Loop Task Group devoted to the quest for a quieter Velcro. This curious and generous engagement with her subjects makes for world-expanding reading, even if it leaves other questions unaddressed — such as the value of investing quite so much effort into the design of more comfortable outfits for snipers.

In “Fuzz,” a similar nearsightedness keeps the lens trained on individual characters while sometimes overlooking systemic problems. Climate change, for instance, makes only two appearances in the book, although nearly every problem she catalogues will be exacerbated by increasing instability in the relationships between humans, plants and animals. Roach is certainly aware of this, but you get the sense that it would be a bit of a buzzkill to point it out; even someone who can so adroitly crack a joke over a corpse may have some trouble with the big C.

This emphasis on the human scale does deliver satisfying payoffs, especially in the way Roach subtly reframes what counts as “wildlife.” The problem with wildlife is that it’s not very wild. Bears peel open minivans and stroll through patio doors because they are part of an increasingly human ecosystem, where food chains include restaurant trash bins and empty summer homes with generously stocked refrigerators. Birds and elephants raid corn fields, mice nibble the insulation off engine cables, and gulls mob landfills for the same reason: because we are a part of their world, and vice versa.

This dynamic is perhaps most neatly summed up in India, where Roach travels to investigate the rhesus macaques terrorizing residents of New Delhi. The monkeys have learned how to raid mansions and kidnap cellphones for banana ransom. No one can decide whether they constitute a city problem or a country one, least of all the people who might be responsible for solving it. Roach meets with the city’s head veterinarian, part of the municipal government, who answers all monkey-adjacent questions by referring to the chief wildlife warden, in the forest department; when she reaches the wildlife warden by cellphone, he refers her directly back to the city vet. Well? Are we dealing with nature or society here? The distinction is, at best, a fuzzy one.

Fuzz

When Nature Breaks the Law

By Mary Roach

Norton.
308 pp. $26.95