The simple explanation -- which I unfortunately left out of my slides but did elaborate on during my talk -- is that Bitcoin has a way for you to send money to

The simple explanation -- which I unfortunately left out of my slides but did elaborate on during my talk -- is that Bitcoin has a way for you to send money to someone contingent on them producing the preimage of a SHA256 hash. The remainder of the script allows you to get your money back if the person doesn't have or doesn't provide the preimage within a certain amount of time. If you use a zero-knowledge proof to enforce that the preimage of the hash is a key which unlocks some data you want, this becomes a powerful tool for building exotic protocols or performing risky transactions. It also doesn't cost much on the Bitcoin side of things.