Dir.glob doubt

[Rodrigo_Rosenfeld_Ro (Rodrigo Rosenfeld Rosas)]

Reading the Rails source, I found this:

(Dir.glob("#{@path}/**/*/**") | Dir.glob("#{@path}/**")).each do |file|

Why is it different from just:
(Dir.glob("#{@path}/**")).each do |file|

What am I missing?

Thanks,

Rodrigo.