I have heard the oft-repeated "fact" that no two snowflakes are ever the same. Having a fair idea of how snowflakes form, (those Last Word books are very educational), I can see how this might be true. But it's still possible for two snowflakes to be clones. What's the probability of two different snowflakes forming the same, and looking exactly the same. And, if a estimation of how much snow has ever snowed is possible, can it be worked out how many snowflake clones there has ever been?