When you think of riding the subway, laughter and joy aren’t the first words that spring to mind. It’s a cramped place full of grumpy people either coming home from a bad day at work or are just generally upset. Many are glued to their cell phones or “wired up” and have no time for anyone else. Yet if you’re lucky enough, sometimes you can find happiness in a subway train. One such moment was captured when a Belgian advertising agency working for Coca-Cola hired an actor to randomly start laughing on the train. With the tagline–“Happiness starts with a...