Pause the game and hold L. Now use these combinations to get the following results:
All weapons: Right, X(2), Y, X.
Invisible mode: Up, Left, Right, Up, X.
Slow-motion mode: Left, Down, Up, Right, X.
Fish eye camera: Left, Up, Right, Down, X.
Beagle holes, footprints, and burns: Down, Up, X, Y, X.
Alternate fade: Right, Up(2), Down, X.
Alternate lighting: Up, Right, Up, Down, X.