No economist could remain unmoved by the brouhaha that has engulfed Herbalife, the nutritional supplements company. The sponsors of football teams such as Barcelona and LA Galaxy, it sells diet drinks and protein bars through a network of small distributors, many of whom recruit, train and supply further distributors. This may be an intelligent way of selling the product through word-of-mouth. But doubters wonder whether Herbalife isn't too reliant on distributors filling their spare bedrooms with protein shakes, which they hope to sell at a profit by recruiting yet more distributors.

In May last year, a hedge fund manager called David Einhorn asked a few pointed questions on a Herbalife investor conference call, wondering how many final customers Herbalife actually had. Herbalife's share price promptly fell by a fifth. Einhorn has a reputation as a savvy sceptic, and had made a very public bet against Lehman Brothers a few months before the company imploded. Another short-seller, Bill Ackman, recently took a large short position, and then argued at great length that Herbalife was a pyramid scheme. Herbalife denies this vigorously.

It's not just Herbalife's reputation that is at stake here: it's that of short-selling, a practice that has been controversial since 1610, when it was banned, after somebody tried to short the Dutch East India Company.