Original purpose: Playing a central role in the chicken-and-egg debate.
Aha! use: Cleaning the hard-to-reach places in bottles and vases. Drop some crushed shells in the bottle, add warm water and a drop of dishwashing liquid, and give it a good swirl.
Reward: Shells that scrape off the gunk you can’t get to, so you can save your elbow grease for the dinner dishes.