As Bill breaks down the science of aging, his correspondents try bizarre beauty treatments and learn how spinach could transform organ transplants.
Derek Muller discovers why Mexico City is sinking, Nazeem Hussain tests his desert survival skills and Bill has a drink with a "water sommelier."
Bill explains how addiction changes the brain, comic Maria Bamford shares her struggles and Cara Santa Maria visits a research lab casino.
Karlie Kloss tours Japanese farms that grow produce without soil to save water and space; back in the studio, Margaret Cho samples meat made in a lab.
In London, mutated mosquitos make a meal of Derek Muller; comic Paul F. Tompkins helps Bill burst a common myth about evolution.
Bill and his guests explore animal behavior that is remarkably human.