You say "package Foo" in two different files. :-)

As I said, this should be very rare. But sometimes you want to add or modify functionality in a package someone else wrote. (I've done this several times in Ruby where I'm changing core classes.)

However there is a more common variation of the same thing. If you take a module and refactor it by using AutoLoader, then our variables are not visible in the autoloaded subroutines, but use vars would be.