# before
    if ($word =~ /$expr/) {
       for my $j (-5 .. 5) {
           $words->{$i + $j}++;
       }
    };
# after
    my $mwords = 5;
    @words{$i-$mwords..$i+$mwords} = 1
       if $word =~ /$expr/;
    # Note: Keys created, but all but first have undef values