“Simple rewards may seem like a good idea, but they often have unintended consequences. Consider the case of Kelly the dolphin, who lived in a marine institute in Mississippi.
To teach her to keep her pool clean, her trainers started trading her fish for any litter she collected.
Kelly soon learned that litter of any size would win her a treat. So when a visitor dropped paper into the pool, she would hide it under a rock and tear off one piece at a time to get more fish. Her response was logical but not exactly desirable.