At the Naughty Dog logo, hold Up + X until the title screen appears. Then, hold Left and press Square, Circle, Square, Start. Now while playing a game, pause and press Down, X(26), Down. If you entered the code correctly, you will hear the sound of a snort. The game will resume. Press Select to display a debug menu.
Enter the following sequence at the password screen for access to all 32 levels, all gems, and both keys. After entering the first line, two more lines will appear.
Triangle, Triangle, Triangle, Triangle, X, Square, Triangle, Triangle
Triangle, Triangle, Square, X, Triangle, Circle, Triangle, Triangle
Triangle, Circle, Square, Triangle, X, X, X, X