Blood vessels in the head tighten to stop the loss of body heat and then relax to letblood flow rise; that sudden rush of blood is what causes the headache.
头部的血管收紧以阻止身体热量的流失，然后放松让血液流动起来，血液的突然涌入是引起头痛的原因。
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The Five-Animal Exercises are well-designed to help blood circulation (循环), and let the energy go smoothly in the body so as to improve the health.