private static function _magic()
    {
        // HTTP_ACCEPT_ENCODING changes on Chrome 54 between GET and POST requests
        // HTTP_ACCEPT should change only in IE 6, so we'll tolerate it
        $magic
            = (isset($_SERVER['HTTP_ACCEPT_LANGUAGE']) ? $_SERVER['HTTP_ACCEPT_LANGUAGE'] : '*')
            . (isset($_SERVER['HTTP_ACCEPT']) ? $_SERVER['HTTP_ACCEPT'] : '*')
            . (isset($_SERVER['HTTP_USER_AGENT']) ? $_SERVER['HTTP_USER_AGENT'] : '*')
        ;

        // This is more sophisticated than just $_SERVER['REMOTE_ADDR']
        $req = grab('request');
        $magic .= $req['remote_addr'];

        return md5($magic);
    }