Farmer Joe doesn´t know what to do. He's stuck out on the backwater moon of Io and he needs to get his livestock down to Jupiter to sell in the market. His ship is so small though that he cant´t fit all of his stock in it. He´ll need to make a couple trips to get them all to the planet. But the greater one eats the medium and the medium eats the small. You must imagine how to transport them avoiding to leave alone the one that eat the other.