I was told once at an in home adult toy party that it had something to do with import/export but I can not remember the details.

I'm not an expert, but I have never seen one shaped like an animal.

To be honest i have no idea but i read somehwer ages ago, its something to do with "ego" like if someone acts like a certain animal they would choose that shape, or its something to with the shape each one gives the feel of. but i think its just people want nice shapes to play with HAHAHAHAH. But u do get what i meen dont u? lol