Clam NFTs can be deposited to farm Pearl NFTs. Every Clam has a lifespan between 5 and 15, this means it can produce that certain number of Pearls before it dies. With each Pearl that a Clam produces, it will also be possible to harvest it for some extra $SHELL. But also with each Pearl that a Clam produces, the chance that the next one is rarer, is higher. So the last Pearl that a Clam produces, which will also kill the Clam, has the highest chance of being a more rare one.