A flash mob is a group of people who come together suddenly in a public place, do something unusual for a short period of time, and then quickly break up.
快闪族，是指一群人突然在公共场所聚集，在短时间内做一些不寻常的事情，然后迅速散开。
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For those of us in the latter group—consigned to coach, bereft of Flash Pass, too poor or proper to pay a placeholder—what do we do?
Alternating between physical and mental activities helps, too, as does increasing the novelty of lessons by blending films, tapes, flash CARDS, and group work.