I almost never have two Perl scripts calling each other. In most cases, either:

• (a) they are integrated closely enough that one (or both) should really be a module, and I end up instantiating one from the other (or a controller script) and calling its methods, or
• (b) they are independent enough that I have them both talk to a database or a file and trigger them independently by some external event.

Just my $0.02 worth ...