We were given crushed eggshells, in capsules, as children.
I don't remember any partiular effect that had on us, but I had perfect teeth until I was 18, when a dentist lied to me.
If you get tired of experimenting, try crushing your shells and digging them into your garden.
You could try digging them in around some Watermelon plants, and not others...see if eggshell enriched soil is different, or if the plants will only take up what they are genetically programed to do.