The Sonic the Hedgehog games had a unique and revolutionary take on the players life bar.  The player must collect as many chaos rings as possible.  Every time Sonic is hit by an enemy, he loses his chaos rings and they go bouncing around the screen.  Sonic must collect back as many chaos rings as he can to replenish his life bar.  If Sonic collects too few chaos rings, the next time he gets hit, there will be fewer chaos rings  bouncing around to collect which make replenishing the life bar more difficult.