What are these??

[Pullet Press]

Blood spots and meat spots aren't uncommon. Both are safe to eat but may not look appetizing - you can remove them before or after cooking if you prefer. You don't see them in grocery store eggs because they candle the eggs for any inclusions.

(But those aren't as good as homegrown eggs, )

 

[aart]

It happens when the cuticle that holds around the egg in the Ovary ruptures a vessel while the yolk is dropped into the tube.

Good description^^^.
I think it's explained in this excellent video, which is worth watching regardless: