Mary Roach's book 'Grunt' explores the science behind the challenges faced by soldiers, such as panic, exhaustion, heat, and noise. She introduces us to the scientists who are working to overcome these challenges. Roach shares her experiences with the U.S. Marine Corps Paintball Team, visits the fashion design studio of U.S. Army Natick Labs, and spends time with amputee actors who help prepare Marine Corps medics for combat wounds. She also explores how diarrhea can be a threat to national security and answers unique questions about the military. This book offers a new perspective on our nation's defenders.