I'm not sure this is true. The shadow ray pass is used to determine how much light is returned to the pixel. So something like: * shoot a ray from the pixel *

I'm not sure this is true. The shadow ray pass is used to determine how much light is returned to the pixel. So something like: * shoot a ray from the pixel * when the ray hits an object check how much light that point receives * bounce the ray according to the hit material properties * repeat the bounces X times and gather how much light the pixel will receive. Because most bounes are in a random direction it's best to sample a pixel multiple times. And ofcourse more bounces give a more realistic global illumination result.