How about this? Can you say 'use a hash array' or 'use "my", not "local"', or even 'you don't need an index counter in a for loop':

sub doLookup {
        local($str,$i);
        $str = $_[0];
# Is this an IgnoredWord?
        for ($i = 0; $i < @gIgnoreWords; $i++) {
                if ($str eq $gIgnoreWords[$i]) {
                        return "";
                }
        }
# Is this a ReplacedWord?
        for ($i = 0; $i < @gOldWords; $i++) {
                if ($str eq $gOldWords[$i]) {
                        return $gNewWords[$i];
                }
        }
        return $str;
}
[download]