I know. That's why I said "I don't know" because those hens can make a mess on those eggs but still, probably just that its a chickeny environment as compared to the one we live in. Again... I don't know... I am just passing on information that I've read somewhere.
Not before you check really close with a flashlight and for pip holes.
If you think you felt bad over chicks dying on their own, I hope you never experience the soul shaking you receive when you're impatient and decide that this chick is dead anyway so you open the shell only to find out it might have lived if you hadn't opened the shell. Ask me how I know... and trust me... my soul DID shake! Thank God that was a long time ago and I learned my lesson.
I want to add that a hen has the same bacteria as the shell does so it's not any thing foreign while we put them in super clean incubators and then touch then with our hands which in turn have touched any number of other things. I also have to say I learned the hard way today that I need to wash my hands before and after handling eggs. I'm fighting salmonella poisoning that either came off the eggs in the bator or from messing with my chickens and ducks. I haven't ate anything recently that would have caused it.