There is no such thing as an "animal soul." It's consciousness. Consciousness may decide to incarnate as an animal--it's just another way to grow.
When the consciousness that was incarnated in an animal is released, such as when that particular body is no longer functional, the consciousness expresses itself just like any form of consciousness would. When in animal form, the consciousness cannot speak but when released, it can communicate just like any other form of consciousness. For example, when my Bitsey passed over and appeared in that photograph, she wanted to let me know it was her so she appeared with the lower half of my face as hers. This was a communication that confirmed to me that it was indeed she in the picture--it was a play on the fact that at an earlier time, I'd made a digital photograph of the top of her head on mine (with Photoshop). Pretty witty, I think.
Why would a soul want to incarnate as an animal? I imagine there are things that can only be learned that way.
I know one thing: I no longer think of "animal souls" as lesser than a human's. It's all consciousness, regardless of what type of body it's in.
Cher