Essays / A comparison essay on two living things - need help for an idea [4]

I have been given a assignment to write a comparison essay on two living things. And as it's required to have a clear reason for the comparing these 2 things, i cant think of any thing but the Cat and Dog topic. But i really dont want to go with that topic because there are hundreds essays about cat and dog and simply because i dont like it. Any suggestion?

Thanks in advance. It will be great help for me.