At an open-air school assembly hall in the dusty southern Vietnamese village of Phuoc Thanh, the consumer-products colossus Unilever is implementing a high-powered strategy to sell more soap: the handwashing dance. It goes like this. Rub your left palm with your right hand, then clap, now right, clap, up, down, thumbs, knuckles, clap. Then repeat, scrubbing vigorously. The 200 or so children present on a muggy May morning, ages 8 to 10, know the routine by heart.