While playing the game, hold [Ctrl] + T. Alternatively, hold [Ctrl] + [Alt] and type "qwerty" while playing the game.
Begin a game and press F until the screen flips upside-down. Then, type "I THINK THEREFORE I AM" and press C to skip to the next level.
While playing the game, type "SAGGITARIANS MAKE BETTER LOVERS".
Note: These passwords correspond to the final level and five bonus levels.