While playing the game, press X(2), Square(2), Triangle(2), Circle(2), Triangle(2), Square(2), X(2), R3. If you entered the code correctly, you will hear a sound. You will gain double reflex with every kill. Note: This code prevents trophies from being unlocked. To prevent this from happening, enable the code, then quit to the main menu. Select "Continue" or "Replay Mission", and you will now be able to unlock trophies with the code enabled.