This trace incorporates heavy use of lighting and reflections to get some cool shadow effects.  
The scene is also anti-aliased to get rid of the jagged edges.
The center shere is completely translucent and there is a texture mapped box behind it to get 
a warped refraction effect.
You can see "hidden" objects by looking at the reflections from the spheres.  
There is a blue and green box and an additional point source.