How to get the Secret Tape: On the last question of the 2nd tape, type 'lamb' at least twice.
(Also make sure you're playing version 1.3 of the game)
I'm writing this here because the secret tape is important to the game's lore, but it's very unlikely that anybody would figure this out on their own, and if you try to google how to get the secret tape, the descriptions of some of the search results contain mini-spoilers.