PHP print_r shows an array, not just text

I'm looking for some help again.

I found these stop words script - I basically remove all the regular words from the string.

<?php
$CommonWords = file_get_contents('http://localhost/stopwords.txt');
$CommonWords = explode("\n", $CommonWords);
$CommonWords = array_map('trim', $CommonWords); // <---- ADD THIS LINE
$keywords = 'The <meta> tag’s keyword attribute is not the page rank panacea it once was back in the prehistoric days of Internet search. It was abused far too much and lost most of its cachet. But there’s no need to ignore the tag. Take advantage of all legitimate opportunities to score keyword credit, even when the payoff is relatively low. Fill in this tag’s text with relevant keywords and phrases that describe that page’s content';
$search_keywords = strtolower(trim($keywords));$arrWords = explode(' ', $search_keywords);
$arrWords = array_unique($arrWords);
foreach ($arrWords as $word) {
 if (!in_array($word, $CommonWords) && (trim($word) != '')) 
 {
 $searchWords[] = $word;
 } 
 }
 print_r($searchWords);
 ?>

The result for the code is as follows:

Array ( [0] => [1] => tag’s [2] => keyword [3] => attribute [4] => page [5] => rank [6] => panacea [7] => prehistoric [8] => days [9] =>) 

How can I format it so that the result looks like this: (without array and numbers)

tag's, attribute, page, rank, panacea, prehistoric, days

thank