When I was young, there was a fish vendor who would come by on his bicycle every morning with the fresh catch of the day. The fish were iced in a basket strapped onto a carrier at the back of the bike. Later on, he exchanged his bicycle for a motorbike, while still retaining the air horn that signaled his arrival every day. A few years later, news spread that the ice used to preserve fish at the dock was high in ammonia. Everyone slowly ditched the fish vendor and started buying fish from the supermarket. Supermarkets were new to us then, and no one knew where the fish came from, so that erased everyone’s worries about ammonia-poisoned fish.