Depending on the specific series you are interested in, "S2E3" may refer to other "natural history" or science-related content:
Titled "Our American Storytellers" , this episode explores the genealogical history of Ken Burns, Anderson Cooper, and Anna Deavere Smith. [S2E3] Natural History
Focuses on prehistoric life, specifically the End-Ordovician Extinction , the first of the "Big Five" mass extinctions where over 80% of marine species vanished. Depending on the specific series you are interested