I can't read the article, but the intro is interesting.

"The authors’ most striking finding is a surge in short sales—bets that a security’s price will fall—of an exchange-traded fund (etf) listed on the New York Stock Exchange under the ticker eis, which tracks an index of Israeli shares. In September an average of 1,581 shares a day of EIS were sold short, representing 17% of the daily total trading volume. On October 2nd, five days before the attacks, a whopping 227,820 shares were shorted, representing 99% of total volume. Rather than reflecting a souring of market sentiment, the increase in activity seems to have come from just two trades."