"To see what a ball-and-socket joint is like, make a fist with one hand. This is like the ball. Cup the fist with your other hand. This is like the socket. Swivel the fist."
This is similar to how a hip joint works.
METAMIA is a free database of analogy and metaphor. Anyone can contribute or search. The subject matter can be anything. Science is popular, but poetry is encouraged. The goal is to integrate our fluid muses with the stark literalism of a relational database. Metamia is like a girdle for your muses, a cognitive girdle.