Why does salty water make hard boiled egg shells more fragile? Boiling eggs in salty water rather than regular water makes the salt react with egg shells making them more fragile. My guess is that it's either sodium or chloride reacting with the calcium in eggs. Can someone please explain what is going on in there, and why the reaction makes the egg shell more fragile?

Here's an example YouTube video this effect is mentioned.
The eggshell is made of calcium carbonate mostly, but the crystal structure is held together by matrix proteins (more references in Wikipedia). Salt creates ionic interactions with the protein molecules, breaking protein-protein interactions, and in this case, probably protein-mineral interactions as well, debilitating the eggshell structure.