quicksilver
/ˈkwɪkˌsɪlvə(r)/noun
mass noun
1- the liquid metal mercury水银, 汞。
1.1
- used in similes and metaphors to describe something that moves or changes very quickly, or that is difficult to hold or contain用于明喻和暗喻水银般变幻莫测的; 流动快的; 难以把握的：
his mood changed like quicksilver.
他的情绪像水银一样变化无常。