This game has unused music.
Outlast is a survival horror game. In order to survive, the player must either run or hide from enemies. Also, jumpscares.
Early Credits Music
When you see your shadow in the floor, you can see your body and a head, but in reality Miles has no head.
While it is technically used, it's never seen in-game, even through the use of hacks. It's invisible by default, so the camera doesn't clip through it. It's not until the ending of the Whistleblower DLC where we can see it in (almost) full detail. You can see it better with the free cam command.