I went out to my barn to check on the muscovies that are hatching (I allow my animals to do natural incubation) and gather up the eggshells. Low and behold, I found an egg inside of another newly hatched duckling's egg. So I pulled the inner egg out and helped it get a good start by taking the cap off for it (it looked like it had been struggling) and set it back under the mom. This was definably an odd thing to happen.
How common are instances like this? I've read about twins where there is two babies in a single egg, but an egg inside of another egg?
This is not the only thing weird to happen with my eggs this year. I had a turkey egg that had formed two membranes on the inside of the egg (unfortunately I could not get to it in time and it had died).