Beitzah 3 - More takes on the egg
Still trying to explain why an egg laid on a Holiday (Yom Tov) should not be eaten, Rabbah says that we need to think of when has this egg completed its growth while inside the hen. This happened on the day before. What if that day was Shabbat? Then we have food being prepared on Shabbat for consumption on a Holiday , and that is forbidden. Why? Because the Torah said, " On Friday they will prepare " - that is, only weekday can prepare for Shabbat or Yom Tov, but food cannot be prepared for Yom Tom on Shabbat, even inside the hen. They asked Rabbah, "Shabbat and Yom Tov do not always occur on consecutive days, so the egg should be permitted then!" He answered that the Sages prohibited this in all situations, because sometimes Shabbat and Yom Tov do fall out on consecutive days.
Rav Yosef said that the egg is forbidden because it is similar to fruit falling from a tree - which are forbidden. But, we may ask, the fruit are only forbidden because we want to stop the people from climbing trees and harvesting the fruit, so that itself is a stringency, why do we need another one on top of it? He answered that the Sages prohibited the fruit falling from a tree and the egg laid on a Yom Tom in one fell swoop.
Rav Yitzchak said that the egg is similar to juice flowing from a fruit. They asked him the same question as above: juice is forbidden only because one might come to squeeze it out himself, so that itself is a stringency, and you are adding another stringency on top of it! He gave a similar answer, that it is all part of one decree.
Now we have four possible explanations for the egg, and the Talmud discussed why each of the proponents does not accept the explanation of the others.
Art: Still Life with Fruit, Bird's Nest and Broken Egg By George Forster