I actually cook our eggshells to feed back. I know a lot of people don't bother, but have you ever smushed up baked eggshell with a wooden spoon? It's very therapeutic. I cook them in a metal bowl, just throw them in while the oven is cooling off after cooking, and then set the bowl on the counter with a wide wooden spoon in it. Everybody takes turns crunching them up as they sit at the bar while I am cooking or they are eating breakfast or whatever...just crunch eggshells and chat, lol. Fun times.