This is related to the physiological structure of chickens. Every chicken has testicles and ovaries. The left ovary of hen is developed and the right gonad is underdeveloped. Under the influence of external stimuli and other reasons, gonads may develop. If the gonads develop, the hen's feathers and cockscomb will change and crow. It is precisely because there is a well-developed ovary on the left side of the hen's body that the ovary can not only lay eggs, but also be an endocrine organ, which can produce some estrogen chemicals (called estrone) to maintain its femininity. If the left ovary shrinks for some reason or surgery, and the undeveloped gonad on the right develops into testis instead of ovary, the hen will crow at this time.