Be careful when using include_once and require_once for files that return a value:
fiddle2.php
<?php
return "Some String";
fiddle.php
<?php
$s = require_once('fiddle2.php');
echo "\n" . $s;
$s = require_once('fiddle2.php');
echo "\n" . $s;
/* output
Some String
1
*/
The second time require_once occurs, it returns 1 because the file has already been included.