my ($ret, $msg) = mysub(
                        'cat' => $val1,
                        'dog' => $val2
                        );

sub mysub {
  my $args = {
             'cat' => undef,
             'dog' => undef,
             @_
             };
  my $cat = $args->{'cat'};
  my $dog = $args->{'dog'};
# do something with them
  if ($ok) {
    return($answer, undef);
  } else {
    return(undef, $error_msg);
  }
}