Longtime listeners know: math is Chris Gethard's nemesis. A real-life mathematician calls in and gives Gethard the most thrilling math quiz ever on a podcast. (We feel safe making that claim.) He also talks about his struggle with substances in college and getting sober. Geth also tells a never-before-heard story about an unusual religious ceremony in the rainforest, which involves hallucinogens and terrible diarrhea.

This episode is brought to you by Burrow.com (www.burrow.com code: STORIES), Talkspace (www.talkspace.com/beautiful), Stamps.com (www.stamps.com code: BEAUTIFUL), and Brooklinen (www.brooklinen.com code: BEAUTIFUL).