The eggs of kosher animals (such as hens) are kosher, while the eggs of non-kosher animals are not. One may not eat an egg if a chick has started to develop, starting from the appearance of the first drop of blood from the embryo. This rule is relevant when an egg could be fertilized (for example, on a chicken farm where hens and roosters are together). In contrast, if blood is found in an unfertilized egg, since this type of blood spot cannot develop into a chick, the egg is permissible after one removes the blood. Nowadays, over 97% of eggs sold in supermarkets are unfertilized, so blood spots are not a concern.
