Odd Hole at sac end of egg-twice in one week!What is wrong?

Hi All,
I have this strange hole in two eggs-twice in one week,this has never occured before
All my hens are worm and bug free,they are all wormed regularly,have spice/mineral powders.

This week I have given them cod liver oil and wondered does it affect them in making eggs like this,both are from Gemima.She appears to be in good health,has all her feathers and normally lays well.

The other thing which happened this week is that I caught next doors cat which had jumped on her back-and tried to maul her! Obviously she was ok and i chased the cat off-it is very ferral like.I am having to keep an eye on them all because of this cat!

I have an electric fence going up shortly!!

I though maybe wither the cod liver oil or the shick of the cat has done this but shall await for your advice-this shall be soo appreciated!
Missie x

Could it have been pecked by a hen or another wild bird?

looks like them 2 eggs were fused together and then parted