Eggs with good, strong shells are easier to pass than shell-less eggs. There are various reasons for a hen to produce a shell-less egg. Sometimes it's just a random hiccup in the production line, nothing to be done there. Sometimes a hen doesn't have enough calcium stored in her bones for shell production, in which case increasing calcium intake will help in a few days. Won't do anything for an egg that is already in the shute though. And some hens may have a defective shell gland, in which case, absolutely nothing you do will ever help.
