More about dented eggs

Casually, today I have seen a Trachemys scripta elegans with egg retention. It is kept in a place without soil and it can't lay the eggs. They have been removed using oxytocine.
There is no male, so, they are infertile.
 

They were nine, three were crushed once layed.

Some of the eggs are dented. Trachemys scripta lay soft shelled eggs.

 

The two next pictures are from the same egg. Originally the dent was on the right pole of the egg. If some pressure is applied with the finger on the left pole, the internal pressure in the right pole increases and  the dent dissappears . A new dent has appeared on the left pole,  the one that received the external pressure.



Dent on the right

If pressure is applied on the left side, the dent on the right side dissappears and a new one appears on the left side.  

When the egg is being layed, one of the poles is out but the other is still in the cloaca.  The half that is in the cloaca is under the external pressure caused by the musculature that tries to push it out. The half that is out of the body is under the internal pressure caused by the content of the egg that is being squeezed in the pole that still is in. When the egg is out, the pole that received the external pressure in the last moment, the last to come out, presents a dent.
If you apply pressure in one of the poles of the Trachemys eggs with all the fingers of a hand, trying to copy the pressure that the cloaca makes when it is pushing the egg out, the dent jumps from one pole to another depending on which pole is submited to pressure. It is quite funny.

I don't know why only one of the Clemmys eggs was dented. Is it possible that the shell of that egg was slightly thinner than the others making it more deformable? Or that for some reason this egg had less internal pressure than the others making it more responsive to pressure?