During play, pause and press R2, Down, L2, Up, Right, Down, Right, Left.
Rear view mirror:
During the ski mini-game, press L1 or R1 to bring up a rear-view mirror.
Pause the game and press R2, up, L2, Down, Left, Up, Left, Right, L2, R2
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Thanks to Revolution readers Hortence Mchooly and Arlond!