In this hour of Radiolab, stories of cross-species communication.

When we gaze into the eyes of a wild animal, or even a beloved pet, can we ever really know what they might be thinking? Is it naive to assume they're experiencing something close to human emotions? Or is it ridiculous to assume that they AREN'T feeling something like that? We get the story of a rescued whale that may have found a way to say thanks, ask whether dogs feel guilt, and wonder if a successful predator may have fallen in love with a photographer.

In tape five, three stories: first, a tale of how the cassette tape supercharged the self-help industry. Second, cassettes filled with history make an epic journey across Africa with a group of Lost Boys. And finally, Simon meets up with fellow Radiolabber David Gebel to dig through an old box of mixtapes and rediscover the unique power of these bygone love letters.

Mixtape was reported, produced, scored and sound designed by me, Simon Adler, with music throughout by me. Unending reporting and production assistance was provided by Eli Cohen.

Special Thanks to: Shad Helmstetter, Vic Conan, Glenna Salisbury, Jerry Rosen, Richard Petty, Sharon Arkin, Angela Impey, William Mulwill for sharing his cassettes with me, and to the British library for sharing some of their recordings from their South Sudan collection, which is housed at the British Library Sound Archive.

Support Radiolab by becoming a member today at Radiolab.org/donate.

In 1983, Simon Goodwin had a strange thought. Would it be possible to broadcast computer software over the radio? If so, could listeners record it off the air and onto a cassette tape? This experiment and dozens of others in the early 80s created a series of cassette fueled, analog internets. They copied and moved information like never before, upended power structures and created a poisonous social network that brought down a regime.

In tape four of Mixtape, we examine how these early internet came about, and how the societal and cultural impacts of these analog information networks can still be felt today.

Mixtape is reported, produced, scored and sound designed by Simon Adler with original music throughout by Simon. Top tier reporting and production assistance was provided by Eli Cohen.

Special thanks to: Alex Sayf Cummings, Martin Maly, Piotr Gawrysiak, Joe Tozer, James Gleick, Jason Rezaian, Gholam Khiabany and Mo Jazi. And to Arash Aziz for helping us every step of the way with our story about Khomeini. And Simon Goodwin for making us that secret code. And to Micah Loewinger to tipping me off to these software radio broadcasts.

Support Radiolab by becoming a member today at Radiolab.org/donate.