 Some obstacles, such as the energy balls and crushing pistons, deal fatal damage with a single blow.GameSpot noted, in its initial review of "Portal", that many solutions exist for completing each puzzle, and that the gameplay "gets even crazier, and the diagrams shown in the trailer showed some incredibly crazy things that you can attempt".Two additional modes are unlocked upon the completion of the game that challenge the player to work out alternative methods of solving each test chamber.