Occasionally found on an egg yolk. These tiny spots do not indicate a fertilized egg. Instead, they are caused by the rupture of a blood vessel on the yolk surface during formation of the egg or by a similar accident in the wall of the oviduct.
Mass candling methods reveal most eggs with blood and those eggs are removed. However, even with mass scanners, it’s impossible to catch them all.
Both chemically and nutritionally, eggs with blood spots are fit to eat. You can remove the spot with the tip of a knife, if you wish.