How do I access module subroutines?

[Jonathan Mast]

I know this seems to be a very basic question, but I cannot figure out how
to access a modules subroutines.

We a module named FOO::BAR in which we access some hashes using this form:
$FOO::BAR::hash1
and it works fine.

When I try to access a subroutine in that same module, using this form:
$var1 = $FOO::BAR::sub1();
it doesn't work!

Any ideas?