More than just an opportunity to break a sweat and maybe have some fun, competitive physical activity like sparring allows people to explore disagreement with respect, according to Janet O’Shea, professor of dance at UCLA, who recently wrote a book about the value of play. “If I’m trying trying to punch you and you’re trying to kick me in the head, we disagree on a pretty basic level. But we agree as to the terms of our interaction. At the end, we shake hands and most of the time we actually mean it.”