Two prawns called Tom and Christian are bemoaning their lot at the lower end of the food chain. You know what says Tom, I wish I was a great white shark. At exactly that moment a mysterious shoal of cod appears and one grants his wish. Christian, scared on being eaten immediately scarpers.
For similar reasons none of Tom's other friends or his family want anything to do with him. After a month or two he decides being a shark's not all it's cracked up to be and goes off in search of the mysterious shoal. Eventually he finds them and his wish to be a crustacean again is granted.
As fast as he can he swims back home and seeks out his friend who immediately quivers with fright at sound of his voice.
It's alright says Tom - I found cod and I'm a prawn again Christian.