Every now & again one of my chickens will lay an egg with a thick layer of shell on the narrow end of the egg. Is something wrong or is this normal? I tried to find one, but I don't have any right now to take a picture of it. I think its the Polish hen that is laying the weird eggs, but since I have 4 different birds, each a different breed, I can't be certain. It might also be the wydonnette.... thanks for any info.