Panic in one big market leads other traders to act like a scared herd of gazelles, running frantically for fear of a lion even if they have no idea what or where the danger is.

ECONOMIST: A week on the wild side

Options traders have also gotten in on the act, with GRPN put volume easily outstripping call volume in the early going.

FORBES: Post Plunge Groupon Options Strategies

First, it reaches institutional and individual investors who are active traders, the first ones to receive and act instantly on the information (the innovators and the early adopters in Rogers Curve).

FORBES: How To Trade Investment Buzz