class Hello
{
// ...
    public function __call($name, $args)
    {
        $methods = get_class_methods($this);
        if (!in_array($name, $methods)) throw new BadMethodCallException("Method $name not found.");
    }
}

try {
    $f->remember('My Friend'); // method doest exist
    $f->say();
} catch(Exception $e) {
    die($e->getMessage());
}