Describe how a pearl is formed inside of an oyster.

The creation of pearls occurs as a defense mechanism in oysters, and in order to understand this process, it is important to understand the structure of an oyster. Oysters are soft-bodied water animals that are covered with two hard and roughly textured shells, which are connected by abductor muscles. The shells are produced by the mantle, which is a thin film of tissue found between the outer shell and the inner soft body. The mantle produces a shiny substance known as nacre, which is used to make the shell.
Pearl creation is triggered when a foreign particle gets trapped between the mantle and shell, which irritates the mantle. In turn, the mantle reacts by producing layers of nacre which coat the particle resulting in a pearl. Cultured pearls are created in the same manner but with human intervention. A pearl farmer manually slits the oyster’s mantle and introduces a foreign particle, which ultimately triggers the pearl creation process. However, it is important to note that natural pearls are very rare and consequently much more expensive when compared to cultured ones.
https://www.livescience.com/amp/32289-how-do-oysters-make-pearls.html

https://www.thesun.co.uk/news/1659183/how-is-a-pearl-formed-how-long-does-it-take-and-how-much-are-they-worth/amp/

A type of Mollusk is an oyster. The oyster has two shells that close to protect the Mollusk's organs. When a foreign object, such as a grain of sand, slides in between the shells it begins to irritate the interior, also known as the mantle. The mantle is the interior layer that protects the mollusk's organs. The oyster identifies this object as a foreigner.
The oyster must defend itself from the foreign object. It begins to cover the grain of sand, or any other invader, with many layers of nacre (also called mother of pearl). This is also what the oyster's shell is made of. This process takes place until the pearl is formed.
This is the natural process of pearl development. The synthetic process is when a pearl farmer implants a foreign object into the mollusk.