At the screen were Gabriel shows his face (after opening the book) and before you press [Space] to continue, press [Up] [Up] [Down] [Down] [Left] [Right] [Left] [Right] [Esc] [Space] to unlock a "Cheats" option, which includes options like "God mode", in the extras section of the pause menu. If you entered the code correctly, Gabriel will wink. Note: Enabling cheat options will prevent achievements from being earned and the game from being saved.