Every time you send something on the internet, it’s a copy. But using new technology, can we make digital goods that are… rare? That’s the question behind CryptoKitties, a new game to buy, breed, and sell digital cats on the blockchain. These cats are more similar to real-world collectibles like beanie babies or baseball cards than they are to cryptocurrencies like Bitcoin or Ethereum. In just the last few months, a whole community of third party sites and services has formed around CryptoKitties. And fans have spent more than $23 million playing along. All of this is made possible by the clever and surprising code behind the game.