to get a gun put in < O  X  O >
Go to the entrance of level 8 & go behind the door. It will say in the bottem left hand corner (LEVEL B2) now press X & you will have a secret level.(i've tested it & it works)
If you are stuck on a particular level (darn level 10 in my case), exit and enter the level again. Once loaded and DURING the flyover sequence do the following:
up, square, triangle, square, triangle, circle, up
This will take you back to the Studio with the sheep from that level.