Instructions
Play through level three, called "Slick Willy's River Boat," until you see a bell. Go to the front of the boat and climb the stairs.
Press "R3" to use the "Free Look" camera. This action allows you a first person view of the area. Use this view to aim at the bell.
Press "Square" to spit goobers at the bell. Hit the bell three times to unlock all the doors.