Filter Code Goes On Which Line?

Folks,

Where on Mini Proxy, on which line, would I add the banned words filter code (the code which you see below) so that, when banned words are found on the proxied pages, then the banned words are substituted ?

Mini Proxy is here:
https://github.com/joshdick/miniProxy/blob/master/miniProxy.php

Filter Code:

<?php

/*
ERROR HANDLING
*/
//declare(strict_types=1);
ini_set('display_errors', '1');
ini_set('display_startup_errors', '1');
error_reporting(E_ALL);
mysqli_report(MYSQLI_REPORT_ERROR | MYSQLI_REPORT_STRICT);

// 1). Set banned words.
$banned_words = array("blow", "nut", "bull****");
// 2). $curl is going to be data type curl resource.
$curl = curl_init();
// 3). Set cURL options.
curl_setopt($curl, CURLOPT_URL, 'https://www.buzzfeed.com/mjs538/the-68-words-you-cant-say-on-tv?utm_term=.xlN0R1Go89#.pbdl8dYm3X');
curl_setopt($curl, CURLOPT_SSL_VERIFYPEER, false);
curl_setopt($curl, CURLOPT_RETURNTRANSFER, true );
// 4). Run cURL (execute http request).
$result = curl_exec($curl);
if (curl_errno($curl)) {
    echo 'Error:' . curl_error($curl);
}
$response = curl_getinfo( $curl );
if($response['http_code'] == '200' )
{
    $regex = '/\b';     
    $regex .= implode('\b|\b', $banned_words);   
    $regex .= '\b/i'; 
    $substitute = '****';
    $cleanresult = preg_replace($regex, $substitute, $result);
    echo $cleanresult;
}
curl_close($curl);
?>