Duck egg day 23 strange spot in egg

[Tng476]

Hi!

This is my first time hatching duck eggs and I am currently on day 23. I quickly candled the eggs this morning and all looked good. I very quickly candled again this evening and noticed one egg has this dark spot that wasn’t there earlier today.
I see lots of movement in the egg still. Can anyone tell me what the spot is? Will this little duck be ok? The little one has always been a vigorous mover whenever I’ve candled it over the last couple of weeks.

Thank you!

 

[Tng476]

Also, the egg smells fine and looks totally normal on the outside.

 

[MeganlovesJesus]

I have the same thing in the bottom of my eggs not sure what it is waste maybe