Strange egg

Don't over think this.
Runt egg.... eat it if you wish, but it is what it is...... usually only once in a long spell, so the documentation is excellent.

 

I wouldn't make an omelet out of it!
Over the years my hens have laid strange eggs. A couple of them looked like yours, my brother claimed that one had had a feather inside it, and others didn't even have yolks. Young hens and older hens have them every now and again because their body is changing a bit.
The proteins in the egg are just misaligned. Nothing serious I'm sure.

 

This link is helpful -
http://www.backyardchickens.com/a/common-egg-quality-problems

 

Fairy egg..Fart egg...Or Rooster egg...Many silly names..Any Bird can produce those..Ick..I would not eat it though...

 

Odd, great pic.

Fairy, fart, rooster, whatever egg......small piece of tissue breaks off near ovary, the reproductive system treats it as an ova(yolk) and forms the rest of the egg around it.
I think this video covers that, it's fascinating anyway, Egg Formation Video.

This looks a bit different tho, might be a malformed or infected ova, given the clear inner sphere. I'd have cut that chunk in the middle in half to see if it was a 'lash egg'(hardened pus from infection).

Hopefully you won't see another like that.

 

Oh.......I would not get too concerned?...