Eww on the partially developed egg! Did a hen sit for a while then? Or is it warm where you live?
We went away for 6 days & I had the kid next door collect eggs everyday.
He must have missed that one because when we got home there was 1 turkey egg in there so we thought she had laid it that day.
Apparently she had been sitting on it for almost a week

Didn't even think to candle it.
Kicking myself for it though because I would have liked her to hatch it. We had to process our tom like 3 weeks before because he was getting mean.