There is a not so pleasant odor in the bator when I open it to add water. I set these on Dec 4th- 36 total Last time I set chicken eggs 29 of the 36 eggs hatched and I never candled or anything and I don't remember a smell. I have hatched chicken eggs once and guinea eggs twice. Both time with no incident. My daughter incubated geese eggs and did have a couple of rotten ones. What makes the difference between an egg that doesn't hatch and doesn't smell and a rotten egg?