The blood which is forbidden is the "blood of life." For an animal, this relates to the blood which goes out during the Shechitah. There is a Machlokes with regard to the blood of an egg. Some Rishonim write that it is only a Rabbinic prohibition that was made so as not to confuse it with the blood of a bird which is forbidden. However, others write that the beginnings of the embryo are considered flesh, and if so the blood in the egg is the entire blood of this embryo and is considered blood of an animal (bird) and is forbidden.

D. Zupnik