The 10 silver keys have to be collected from their magnetic clips on the roof of each chamber. Beware of the vents on the ceiling which will occasionally deliver boulders, and mutant pods. These will kill you if they touch you. Use the jet-pac to jump some of the larger gaps in the floor. Don’t  fall through though – the fall could be very bad for you! At the start of the game you can select the difficulty level (1-5), 1 being the easiest. To freeze the game press Select and A to unfreeze.