On Night 5, Spoiler:instead of getting the usual message from the previous night guard (as it was revealed in Night 4's call that he was killed) the player will instead hear some deep garbled speech. When played backwards, it is revealed to be an excerpt from the book, "Autobiography of a Yogi", specifically the section about a scientist who is discussing his theory about plants, animals and metal having a similar life force.
Contributed by Boyobmas