Short-sellers: sound and fury - FT.com Rebellion is hard to keep up. Biting the head off a bat on stage works brilliantly. But how to follow up? The high-profile short-seller has a similar problem. Maintaining a market-moving reputation requires ever-bigger targets. Carson Block's Muddy Waters Research, which once chewed on flighty Chinese companies, wants to move up the food chain. Its latest report, out last week, is on American Tower, a US cellular mast operator with a $30bn market value. The note contains arguments that might appear in any bearish report, spiced with two sharp points about the company's accounts. American Tower's chief executive, we are told, is a big seller of its shares. Real estate investment trusts - a structure American Tower just adopted - are in a bubble. Foreign profits will be hard to repatriate and currency exposure, unhedged. Wireless infrastructure is shifting away from masts. The company has overpaid for debt-funded acquisitions. Interesting, non-scandalous stuff. The spicy allegations are that the company may have fraudulently overstated the price of an acquisition in Brazil by $250m and that it entered sale-leaseback deals which are, in effect, loans - temporarily pumping up rental revenue. American Tower has offered a detailed response to the fraud claim; said its accounts were audited; and disputed other charges. The market has shrugged: the shares are off just 3 per cent since the report came out. If Mr Block's more exciting claims turn out to be empty, using them to get attention for a sensible but dull sell report is dirty pool. That said, noisy short-sellers should be given leeway. Two equity bubbles in the past 15 years have caused real economic damage and sceptics on stocks are still drowned out by a vast cheering section. Investor activism can work - witness Gulf Keystone. The more bat heads that get bitten off, the better.