Pearl harbingers are people who harvest oysters for their pearls. Oysters are mollusks that produce pearls when they secrete a substance called nacre around a foreign object, such as a grain of sand, that has entered their shell. Pearl harbingers dive into the ocean and search for oysters to harvest. They then open the oysters to see if they contain a pearl. If a pearl is found, it is removed from the oyster and sold.