Today I discovered my Embden's first nest of eggs (yea!) but they are all pretty dirty. I've tried to clean them as I would like to sell them but can't seem to get all the dirt off. Is this normal? Are they even safe to eat? I can't figure out how they would get so dirty. They made the nest in a little A-frame I built for them and although it has no floor, I spread straw on the ground for them. Any ideas?