This is a stone egg. It really is a rock. If you get it wet it looks like it glows. It used to be one of those things you buy as a kid because it's cool. Now it's in the hen house.
Why is it in the hen house?
Let me put my teeth in and I'll tell you a story from my childhood....
*insert sloppy denture insertion noises*
Back when I was knee high to a grasshopper and bread was... probably less than a dollar. I wasn't the one buying the bread so I have no idea how much it was. It was just always on the counter and I was aloud to eat it.
Anyway. We had chickens. And I remember someone, who was taller than me which means they were older, said to put a round drawer knob in the nesting box to stimulate their laying instincts. Well I don't have anything with a round knob, but I found this stone egg in a random place. So I put in the nesting box. We will see how it goes.