We gathered eggs yesterday morning, and I found one that when you shook it a tiny bit it felt hard inside. I thought perhaps there could be a developing chick inside, which would be difficult considering we don't have a rooster. When it was cracked and put into a measuring cup to check it out, nothing out of the ordinary, other than the membrane was super hard to open. No bad smells. What on earth made the egg feel like it was full of rocks?