I've got three duck eggs in my incubator on day 27. The air cell in one of the eggs has turned really dark, just by looking through the incubator I clearly see it, looks like there is black on the inside of the egg where the air cell is. It's been that way for two days and I can't find any info on it. If it's dead, how long until it will start to stink? I'm keeping a close eye on them and smell the ventilation holes every time I check, I don't smell anything rotten. Being so close to hatching (hopefully) I don't want to mess with it, but don't want it to explode on my other eggs. Any info is greatly appreciated, I tried to get a picture but it's difficult through the incubator lid. Thanks!