Tongue First: Adventures in Physical Culture by Emily Jenkins An Owl Original/Henry Holt and Co.$14.95, 242 pp. Why do we do the things we do? Why do people pierce, ink, drink, aerobicize, manicure, decorate themselves or even nap? And what, if anything, do these activities say about who we are? These are the questions author Emily Jenkins asks, and sort of attempts to answer, in Tongue First: Adventures in Physical Culture. The book is a documentation of her own efforts to understand, firsthand, why we do what we do to -- and with -- our bodies. "I have always been curious -- but I think most people are. We just don't all take the time to explore or examine our curiosity," she writes. With that in mind, Jenkins puts herself through a full range of bodily experiences, from the pleasant to the painful, the odd to the outrageous. In the name of research, she gets tattooed; snorts heroin with friends; gets Rolfed and stuck with acupuncture needles; deprives herself of sleep; experiences sensory deprivation in an isolation tank; shaves her head; goes to a strip show, the doctor and a nude beach. All the while, she chronicles her reflections and feelings as she pushes her own limits. "I was looking to broaden my experiences and cross some of my boundaries. I picked heroin because I was afraid of it, and I thought it was important for the book to consider my fears as well as my desires," writes Jenkins. Some might not recommend snorting heroin for book research, but that attitude illustrates one of the key social standards Jenkins examines: the need to make a distinction between different forms of the same thing. For example, she explains, social conventions say that a few drinks at happy hour is fine, but doing heroin isn't."The luxury of the cocktail hour and its ritualized consumption create an altered reality that is safe because it's shared, unremarkable because it's so accepted," she writes. "It is also legal. Illegal drugs have more covert rituals, less charming paraphernalia. More important, they don't have the classy history of the cocktail hour casting a sophisticated glow over their recreational use." When she's not questioning social authority, Jenkins discusses her own neuroses. For example, despite her convention-defying experimentation, she confesses how, when trying on a dress that she loves, she decides not to buy it because it doesn't fit the social convention: Society says to wear a dark dress to an evening party; the dress is yellow. Throughout the book, Jenkins describes her experiments starkly, neither glamorizing nor denouncing. She states frankly what each experience did -- or didn't -- do for her, and moves on to the next adventure, not preaching, and sometimes not learning anything more than, "That didn't do much for me" or "I didn't really like that." For example, she admits her boredom in the isolation tank. While she's heard that others see God in such situations; she sees "something very close to Schoolhouse Rock." For all of her bravery and sense of adventure, there is at least one frontier she wasn't ready to explore: the high colonic. "I should say up front that I am not going to get a tube stuck up my ass for the sake of literature," she writes. "I am more afraid of the colonic irrigation machine than I was of doing heroin, so much so that I am perfectly willing to talk about it from a standpoint of total colonic virginity, no matter how revealing it is about my neuroses, my sexual practices, and my general cowardice." It's this pragmatic approach that makes her acts, no matter what our own boundaries, easy to relate to. Even if you'd never cross-dress or shave your head, you'll find familiar ground here: After all, we all have bodies, and what we choose to do with them helps define who we are. As Jenkins points out, all of our costumes and habits, whether innocuous or extreme, speak equally loudly if we only will listen. And they say different things for each of us. We all do things with and to our bodies -- and do them for our own reasons. As to a definitive answer why, Jenkins certainly isn't going to tell. She states unequivocally in the first chapter that she is not going to attempt to explain what life lessons she has learned, or how she's become accepting of everyone and everything, because, she admits, she hasn't. The book is simply about her own self-exploration. What she does, however, is invite readers to "Stick out your tongue and taste the wind as it goes past." It's not an easy invitation to turn down. For excerpts from the book and other writings by Jenkins, visit her Web site at http://www.emilyjenkins.com.