Crabs in the dirt make a great foundation for a seaside hut. It's right on the seashore, where all the crabs dig their holes in the dirt. But as they get old and die, their bodies form a strong base. Perfect for the foundation of a building like this!
Remember, a good foundation is the key (き) to a good house. No, literally. You have to use a piece of the foundation to make the key to your house.