Oysters (and a few other shellfish) create beautiful pearls as a sort of bodily defense mechanism. Learn how it works in this episode of BrainStuff, based on this article: https://animals.howstuffworks.com/marine-life/question630.htm

Why Is Siberia's Batagaika Crater Known as the Doorway to Hell?
11:10

BrainStuff Classics: How Would Authorities Handle a Murder in Space?
08:17

How Does Taste Work?
13:59