Here's a variant, if anyone's interested:
-Instead of two chickens and a fox, you have a fox, a rabbit and a basket of carrots.
-If the fox and the rabbit are left alone, the fox eats the rabbit.
-If the rabbit and the carrots are left alone, the rabbit eats the carrots
-You still can only carry one thing at the time (the basket with the carrots counts as "one" thing)