In the PS3 game The Unfinished Swan, there is a menu that looks like a book, with one page for each of the five chapters of the game (completed parts can be re-played from this menu).
There is an additional page titled "Extras" that contains three items: "Credits", "Concept Art", and "???".
What is the third menu item on the Extras page? I think it has to be unlocked to be accessed, but how do we unlock it?