How Pearls Are Formed Naturally

It can be amazing how extraordinary things happen as a result of ordinary activities we often overlook. One of such wonders is how pearls are formed as a result of oysters, mussels and clams' protective mechanism against unwanted organisms. Click on the link below to see video
 https://www.youtube.com/watch?v=T18E58vOTus&feature=share

And now this is what we have thanks to the activities of these creatures.