A Russian friend of mine once told me a joke: aliens have abducted a Russian, gave him two perfect steel balls, put him in a perfect empty room without doors or windows and told him to come up with a trick to entertain them once they return in a week. They threatened to disintegrate him if he fails to amuse them. Once they returned and asked him to perform the trick he invented he told them he's sorry but he has broke a ball and lost the other one.