'Grunt' tackles the science behind some of a soldier's most challenging adversaries -- panic, exhaustion, heat, noise -- and introduces us to the scientists who seek to conquer them. Mary Roach dodges hostile fire with the U.S. Marine Corps Paintball Team as part of a study on hearing loss and survivability in combat. She visits the fashion design studio of U.S. Army Natick Labs and learns why a zipper is a problem for a sniper. She visits a repurposed...