Blood vessels in the head tighten to stop the loss of body heat and then relax to let blood 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。
2
Waving can mean welcome and farewell, whereas scratching your head may indicate that you are at a loss.
挥手表示欢迎和告别，而挠头则表示不知所措。
3
The financial rescue plan passed by the US Congress is viewed as flawed but necessary to head off panic in financial markets and loss of confidence in the economy.