no, it wasn't rotten. Sometimes if there is any weakness to the shell, a small fracture, something like that, just the normal wear and tear of setting makes it break. Next time try candling the eggs before you put them under her in a really dark room to see if you can see weak spots or cracks. I...
WOW! Looks like she is real serious about those eggs! What a great video! The big tan eggs, the one on the left is from my clean legged splash marans with the black rooster. It is a full sibling egg to the one that hatched this GINORMOUS chick earlier this week.
The egg next to that one is...