BEIJING—As Chinese markets vacillated one day last month, Zhang Jie stood in a stock-trading hall and did the natural thing: She danced a stiff-armed shimmy reminiscent of the Macarena.

Afternoon trading had begun, and people were trailing in from the cold. After a spirited game of cards and a prolonged snack of home-pickled vegetables, 58-year-old Ms. Zhang was in a good mood.

“Is today more volatile than it was yesterday?” she called across the hall to a retiree by a computer.

The man nodded.

“Got it, brother!” she shouted back, then returned to chatting with friends.