PHP - Figuring Out Censor.php

So I have been reviewing my codebase that i stepped away from for a couple of years.  Surprisingly (or not), so far I understand almost all of my code.

But I have a function that **** out dirty words, and there is one section of the code that isn't making sense.  (I added var_dumps, but I'm just not seeing what it is doing.)

Below is slightly simplified code - since my real code uses the database plus a bunch of words I can't post here!

I have added comments where I'm hung up...

<?php
  // Initialize Variables.
  $patternsArray = array();
  $replacementsArray = array();
  $tempArray = array();
  $matchesArray = array();
	  
  // Un-censored text.
  $text = "Cassie, slipped on some glass and cut her ass!<br>
           'Goshdamnit! Who left this damn mess out?' she cried.<br>
           'Well, SHOOT, you should be more careful!' Mary laughed.<br>
           'Hello! Why don't you clean up after yourself!' Cassie screamed.<br>
           'Go to HELL!' Mary yelled back.<br>
           Then suddenly, blood started shooting everywhere.";
	  // Create Replacements.
  $replacementsArray[0] = '***';                  // ass
  $replacementsArray[1] = '****';                 // damn
  $replacementsArray[2] = '****';                 // shoot
  $replacementsArray[3] = '****';                 // hell
  
  
  // Create Patterns.
  $patternsArray[0] = "/\b(ass)(s?)\b/i";       // Word pattern
  $patternsArray[1] = "/damn/i";                // Substring pattern
  $patternsArray[2] = "/\b(shoot)(s?)\b/i";     // Word pattern
  $patternsArray[3] = "/\b(hell)(s?)\b/i";      // Word pattern
	  // Sort Arrays.
//  ksort($patternsArray);
//  ksort($replacementsArray);
	  // What does this do????
  foreach ($patternsArray as $pattern){
    preg_match_all($pattern, $text, $tempArray, PREG_PATTERN_ORDER);            // (1)
//    preg_match_all($pattern, $text, $matchesArray, PREG_PATTERN_ORDER);       // (2)
	    $matchesArray = array_merge($matchesArray, $tempArray[0]);                  // (3)
    /* If I comment (1) and (3) and uncomment (2),
     * then var_dump($matchesArray) displays nothing.
     * Not realy sure what this block of code does...
     */
  }
	    // Clean text.
    $cleanText = preg_replace($patternsArray, $replacementsArray, $text, $limit=-1, $allCount);
	  ksort($matchesArray);
  
  echo "<b>DIRTY TEXT:</b><br>
        $text";
  
  var_dump($patternsArray);
  var_dump($replacementsArray);
  var_dump($tempArray);
  var_dump($matchesArray);
  
  echo "<b>CLEAN TEXT:</b><br>
        $cleanText";

?>
	

In the test I run locally - again I couldn't really post that here - my function seems to work, but I don't see how the parts i commented above work/help get the end results I want.

The goal of reading all of my code line-by-line is to UNDERSTAND it, so that when I go to code my final module, I know my head is in the game.

Thanks.