I throw the weak shelled or odd eggs back down to my chickens right in the coop or outside in front of their coop.
It is an old wives tale that it will get them in the habit of eating their own eggs. That just isn't true.
I throw the whole egg down and it breaks on the ground in front of them, they run up and eat it.
I have had chickens for many years and out of the 500 plus I have now (I am currently down a few hundred), no one eats eggs unless they have low protein problems.
I have never, ever had a chicken eat their eggs because of low calcium but I always make sure they have oyster shell. They may need more protein and bust an egg for that or if they see a cracked one they will get rid of it as it is their instinct to get rid of it before it draws a predator.
I can lay eggs on the ground and they all run over to it and then look up at me to bust it for them. If I tap it they do too but they never bust it.
I never heat the darn things either. Waste of time. They can eat their own shell fresh or old. I bust the undeveloped ones from my bator and they eat those shells, too. No one has been sick from it.
Just my many years of experience with chickens and eggs.