print
    join( '',
          map( "$_: $word_count{$_}\n",
               @gt_three_char_words[ 0 .. 9 ] ) )
    . "\n";
[download]

No offense intended, but that is truly ugly. Why not a simple for loop:

for my $word (@gt_three_char_words[ 0 .. 9]) {
   print "$word: $word_count{$word}\n";
}
[download]

Now here is how I would have written the entire thing.

You've got a couple of errors there: $word where you meant $_ in the increment loop and an extraneous ( after split.