On the main menu of the DVD where it shows behind the scenes, art gallery, etc, do not do anything. Just simply wait. Soon, you can hear a voice of a soldier begging you to press play.

On any section of the DVD(NOT watching the movie, just the sections), press and hold the left button on your DVD remote. It should cycle quickly through the selections of the section and soon, it will send you into a secret art gallery. Each section gives a different gallery.