In ancient India, there was a popular saying: When an oyster opens its shell, the raindrops from the sky fall into the shell and turn into a dazzling pearl. In fact, the real cause of pearls is small insects and gravel. Other foreign objects accidentally fall into the shell, which stimulates the epithelial cells of the shell's mantle. Then it develops into a pearl sac, which continuously secretes nacre, and then surrounds the pearl sac. Over time, a pearl is formed.

Nowadays, artificial surgical methods are used to cultivate pearls. It is impossible to determine whether the mussel has pearls from its appearance. Unless... it is examined with an X-ray machine!