Mary Roach writes books about science that have a sense of humor. She’s written eight books, including “Stiff,” about human cadavers, and “Bonk,” about the science of sex. Roach’s latest book is “Grunt: The Curious Science of Humans at War.” She talks this hour with actor and author Benjamin Busch. He asked Roach about her beginnings as an author, writing press releases for the San Francisco Zoo from a trailer next to the gorilla exhibit.