One of the earlier rear suspension designs.  Dan Hanebrink took the SE front triangle and grafted his rear suspension onto it.  The quick release lever mounted on the top of the shock is used to control the damping.  The tighter the quick release, the slower the shock movement.  The owners manual suggests filling the shock with water in case you lose air pressure.  In the middle picture below, you can see the plastic piece mounted to the chain stay to keep the chain from bouncing into the tire.