While going through the rooms with all the Marines, stop in the second room next to the projectors. Look on the left hand side of the table that they are on. You should find a button there. Face it, and press ACTION. It should switch the screens that the projector is on. Repeat this, and eventually something else will appear on the blank screen. Continue pressing the button until it cuts to a sequence where Snake keeps pressing it. Note: Eventually something will happen and you will be caught and fail. Also, pay attention to which screen the Marines are looking at for an added laugh.