OK, here is the bit of code in question.
/**
     * Internal method which performs sending using predefined list of params.
     */
    protected function _send($sEmail, $sSubject, $sBody, $sParams = '')
    {
        $aParams = array();
        if(!empty($sParams))
            $aParams = unserialize($sParams);
        return call_user_func_array('sendMail', array_merge(array($sEmail, $sSubject, $sBody), $aParams));
    }
}