Candle?

[Vanitychickens]

What does this look like to you dont be fooled

 

[Ebony Rose]

Could be fertile and midway through the brooding process. Could have once been fertile, started the brooding process and then quit (died). Could be a rotten egg.
I don't see any blood vessels.

 

[cmfarm]

Looks rotten.

 

[Mvan42]

Could be as the above post said, rotten, I don’t see vessels so probably not mid incubation, or just dark from the way it is being candled against the other eggs. Those are my guesses.