PHP：使用共享方法链接的方法

Here's something that I've been thinking about for some time. I want to chain together a set of methods like in the below shown example.
The concept of method chaining is no brainer, but what I want is to make all of our animals be added through the same add method, so how should I figure out what type of animal that we're adding inside the add method?

$zoo = new Zoo;
$lion = $zoo->lion->add('Lucas the lion');
$cockatoo = $zoo->cockatoo->add('Chris the cockatoo');

class Zoo {

    function add($name) {
        //How to figure out if the animal is a Lion or an Cockatoo?
    }

}

One solution to the problem would be to override __get in the Zoo class to return a 'creator' class.

function __get($animal){
    return new Creator($this, $animal);
}

Then let the creator class call the add function in the zoo class.

class Creator{
    public function __construct($zoo, $animal){
    ....
    }
    public function add($details){
        $zoo->add($this->_animal, $details);
    }
}

This solution is fairly ugly, and from a future developers perspective, not that clear. As pointed out in the comments, there are better ways about going this. Doing something like:

$zoo->add('lion', 'whatever')

or

$zoo->add( new Lion('Whatever') )

May be a better solution and in my opinion it is far clear to other developers what is happening. (This may not be the case for you, as I don't know the details of exactly what you are doing).

Since we're talking about Object Oriented Design it would be much more "correct" and flexible to implement hierarchy like:

interface IAnimal {}
class Lion implements IAnimal {}

class Zoo
{
    private $animals = array();

    public function add(IAnimal $animal)
    {
        $this->animals[] = $animal;
        return $animal;
    }
 }

 $zoo = new Zoo();
 $lion = $zoo->add(new Lion('Lucas'));