Second shell?

[NevadaRon]

Occasionally I'll find an egg that looks cracked, and I'm thinking it's a loss. But on closer inspection there is another shell over the egg that is cracked, usually only partially there (not completely covering). Has anyone else experienced this? If so, what is happening?

 

[ChicKat]

sounds like it gets a crack while the egg is in the ovaduct and the shell making process tries to fix the problem.