I don't like the package %files there. You can get rid of it by passing a closure to File::Find...

sub find_duplicate_files {
  my %dupes;
  my %files;
  find sub {
    -f && push @{$files{(stat(_))[7]}}, $File::Find::name; 
  }, shift || ".";
  ....
}
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Much cleaner. Easier to maintain. Smaller locality of reference. Blah blah blah. {grin}

-- Randal L. Schwartz, Perl hacker