I heard a duckling peeping from the incubator room. But I looked in the incubator and none had hatched.
I heard the peeping again. It came from the back of discarded incubator eggs that I took out of the incubator when they failed to hatch.
The egg was getting cool and the duckling had only made a little hole in the egg. I put him in the incubator.
This morning I see that he hatched. If he survives ducklinghood, I'm going to keep him.