Grunt: The Curious Science of Humans at War gives its readers a glimpse into the fascinating and often bizarre world of military science. Beginning with an anecdote about the "chicken gun"—the massive, artillery grade gun that shoots frozen chickens at jets to test whether the windshields can withstand high-velocity collisions with birds—the book sheds light on the unexpected, innovative solutions scientists have come up with to tackle the unique problems faced by the military both on the battlefield and off.

In the first chapter of Grunt, Mary Roach visits Natick Labs, also known as the US Army Natick Soldier Research, Development, and Engineering Center. The "flame goddess" Margaret Auerbach leads her on a tour of the Ouellette Thermal Test Facility, where Roach witnesses a test on various swatches of fabric. Each fabric burns in a different way (polyester, for instance, melts, adhering to the skin, while Nomex, the material used in firefighter uniforms, will give wearers up to five extra seconds before catching fire; unfortunately, it's hard to print Nomex in camouflage).

The scientists at Natick Labs are also researching liquid-repellent fabrics. Roach watches ketchup, coffee, and milk roll off a patch of camouflage fabric. She's amazed by the combination of science and design that goes into all forms of military clothing: buttons, for instance, must meet minimum compressive strength standards, and zippers are a liability to snipers (the reflective metal can give away their position). This brings up the broader question of safety, which leads Roach to examine the different kinds of protective gear available to the military.

Annette LaFleur, the Army's top fashion designer, tells Roach that style and feel are as important as function, if not more so. "With protective gear especially, it's key that you design something that's kind of cool and sleek, because otherwise they're not going to want to wear it." This can mean the difference between life and death. There are many different kinds of protective gear soldiers wear: body armor, helmets, ear plugs. In combat, any part of the body can be injured, including the heel, which poses one of the most complicated problems for scientists.

WIAMan—the Warrior Injury Assessment Manikin—was designed to help researchers study one of the most common injuries soldiers face: deck-slap, which occurs when an IED detonates from below and knocks soldiers in their heels, causing various foot, leg, and spine problems. WIAMan is so lifelike that it's able to mimic the hyper-specific injuries soldiers receive in an explosion, all the way down to the tendons that are affected. It's still being tested, however, and the bureaucracy behind military research leaves something to be desired. Getting official approval for projects like WIAMan can take years—especially when that research could, theoretically, be done with human cadavers.

Roach doesn't shy away from the more grotesque aspects of military science. In addition to being present for a test explosion that uses (donated) human cadavers, she's also present for a procedure in which a medical researcher removes a cadaver's penis in hopes of transplanting it onto a soldier who has been wounded in battle. Such "below the belt" injuries are not uncommon in the military but aren't that widely discussed. Genital transplants come with their own host of problems, however. In addition to the medical difficulties (of the host rejecting a transplant or a new transplant failing to function properly), there are legal quandaries, i.e. does the last batch of donor sperm belong to the donor's family or to the recipient's, and if said donor was a soldier, would the child resulting from an insemination of the sperm become a military beneficiary (receive the soldier's pension)? These are sticky questions currently being debated.

Genital transplants may be the most intriguing medical procedures detailed in Grunt, but aren't the grossest—that dubious honor goes to the "maggot treatment," which involves introducing blowfly larvae into a wound for the purpose of debridement. In 1928, a physician by the name of Dr. Baer realized that maggots, natural consumers of dead flesh, could be used to clean wounds of necrotic cells and debris that is difficult to remove surgically. Since then, the "maggot treatment" has been prescribed sparingly, but with impressive results. Soldiers, as it happens, are hesitant to receive the maggot treatment or to "mess with Nature"—the reason one Navy SEAL gives for refusing to take anti-diarrhea medicine, despite proof that Nature could kill him.

One of the best things about Grunt is that it forces the reader to think about what it's really like to be a soldier. In the introduction, Roach makes it clear that this book isn't about the advanced weapons the military has been developing (that "chicken gun" is the only gun she really dwells on). Instead, she focuses on the human side of war: what soldiers eat, in what ways they're wounded, and, most importantly, how they stay alive. Fighting diarrhea is one of those ways. Combating hyperthermia, dehydration, and heat stroke is another (as detailed in the chapter "Sweating Bullet"). Medical and military science is, first and foremost, striving to keep people alive—not kill them. It's preventing soldiers from losing their hearing. It's helping them sleep. And, in the case of combat medics, it's teaching them to cope with the stress of working in the middle of a battlefield.

Sometimes, however, military science doesn't help (or doesn't bother to). Roach points specifically to the Navy. In the ocean, sailors have three primary enemies: the Enemy, the ocean itself, and the living and working conditions on submarines. Sailors divide their days up into "sixes"—six hours of watch, six hours of other duties, and six hours of personal time (only some of which is used for sleep). This leads to exhaustion, impaired mental capacity, and stress, but in spite of many studies showing that this is detrimental to sailors, nothing has been done to change the system. The reality is that these conditions keep the sub running and, thus, keep the sailors safe and alive. Roach even quips, "Better dead-tired than dead."

The living, however, have much to learn from the dead. When a soldier (or a dog) dies in combat, their body is autopsied, and their manner of death is examined in detail. Did the recently designed medical device help in any way? Was the needle long enough to slip through the muscle of a well-trained soldier's pectorals and reach the lung that collapsed? Answering such questions is essential to keeping future soldiers alive. Still, when you're in the autopsy room, staring at all these soldiers cut down in their prime, it's hard to justify their death. War doesn't seem like reason enough for all this killing. In the end, Grunt questions whether or not war is ever justified.