I have raised small flocks of chickens for over 30 years now & every now and then I'll get an egg that is not perfect. I had one of those eggs recently. One good thing is that I had only one egg and not a series of eggs. I take that as a sign of no major infection concerns. I could be wrong but I see no signs of illness. This egg is wrinkled or Corrugated shell ( I believe more the latter) From what I can find out... that is most likly a stress related cause by being an overly large egg (which it is) or having two yolks release by the ovary relately close together. For more imformation to can go here that is a PDF of 20 common egg shell problems and here at Backyard Chickens website on Common egg quality problems. I hope this helps anyone who on occasion come across an egg that is not perfect. I know it helps me. Another good resource is "The Chicken Encyclopedia" by Gail Damerow. Its a good general infor...