The day I left Vietnam, I laughed and laughed. I had not expected to. I woke up feeling sad about having to leave after only two weeks: far too short a time for my first visit to this captivating country. But my travel-mates—Anne and Lindsay, close friends I have known since freshman year of college—and I had hatched a plan for our final morning: we would get up at 5:30, throw on clothes, and walk over to Hoan Kiem Lake, a short stroll from our hotel in Hanoi. Anne had done this the day before. “Trust me,” she said. “You won’t believe it.” As we neared the lakeshore, the streets filled with people, many in athletic outfits, walking, jogging, bicycling. They, and we, were reveling in the relative cool of the dawn  air: by 9 am, we all knew the temperature would be in the 90s and indescribably humid. When we got to the lake, we saw exercise groups of every possible type, all of them already in full swing: Tai Chi, yoga, Zumba, old-school aerobics, hip-hop dancing, ballroom dancing. Across the street, a few dozen people had gathered with the apparent purpose of laughing their heads off. The laughing people motioned to us to join them. Why not? “Ha, ha, HEE,” we all shouted in unison, as we stretched and moved in gentle yoga-like ways, following the leader as best we could; breaking into more free-form laughter as we formed into a shoulder-massaging congo line; and then making different laughing noises as we clustered in [...]