every once in a great while from one of our laying hens we've gotten an egg that just has the membrane & no shell! does anyone know what could cause this? they are very well fed chickens & are healthy. most are between 1 year and a 1.5years. there is a couple that are a bit older but still young enough to still be laying daily. It only happens once in a great while. over the last year we've gotten 3 eggs like this. It is just very weird & was wondering if anyone knew WHY?