If you look at the squares. You’ll see a really dark spot. Well, if you look at the square on the “8”. You’ll see a dark spot too. If I move the egg back and forth. They both move.
Is it a large egg? Could be. Too hard to tell at this age. I definitely see good development in the bottom box.
Keep in mind there are other things in the egg. Like blood spots. Without seeing it in person who knows. But I do love a good mystery. Post an update for sure.