A master fed his dog an egg everyday. One day, the master took the dog to the seashore and started running. While running, the dog saw something white and round. He mistook the oyster for an egg. The dog wanted to eat the 'egg'. Without wasting a minute, he excitedly ran to where the 'egg' was. He opened his mouth and swallowed the oyster at once. Then the dog continued on his way. But after some time, his stomach started aching. The dog thought, "I eat an egg everyday, then why is my stomach paining only today?" It struck him that maybe what he had eaten was not an egg.