One of our hens was sat on 15 eggs until day 20. In the morning of day 21 I couldn't find her anywhere near the eggs and they were stone cold, some had pipped a little. I quickly put them in our incubator which was running as I'm incubating some duck eggs at the moment. One is in the process of hatching (pipped 24 hrs ago). My question is about one of the ones that had pipped. Theres now a crack running in a circle down the egg. Its not like its been zipped as the circle runs length ways. The shell is slightly hanging off and through the gap it looks like the membrane is intact completely. Theres no movement at all. I'm wondering if its possible the chick has started to decompose and the process has caused the shell to come away? Or is this just a weird hatching? Thanks for help in advance.