The food that hens eat always contains a lot of calcium, especially during the laying period. If a hen lays double yellow eggs, it means that its reproductive system is abnormal. When this happens, the ovarian function is overactive, and the mature eggs are continuously discharged to the fallopian tube, which makes it too late for the fallopian tube to wrap the yolk with protein, so the two yolks gradually approach and finally are wrapped in the same eggshell, becoming double yellow eggs. In fact, there is also a kind of non-yellow egg, which is also produced under abnormal circumstances. Because the fallopian tube will secrete protein and eggshell from the falling things, and wrap it up. However, if a hen has parasites in her ovary and accidentally falls into the fallopian tube, or a local blood vessel in the ovary or fallopian tube ruptures and a blood clot falls into the fallopian tube, it will be wrapped by protein and eggshell to form a yellow-free egg.