If you happened to have stepped away at 12:30 or so, you might be surprised to know that the Dow fell more than 200 points. Well, maybe not so surprised any more. Volatile, last-minute selloffs have become an unsettling pattern on Wall Street - more than a third of today's decline happened in the last 10 minutes of trading. One big explanation could be hedge funds and other deep pocket investors that have to sell stock in order to meet margin calls. The more they sell, the more the market goes down, leading to still more margin calls and the need to raise cash. "Somebody must have realized they had to make some sales here at the end of the day," Todd Clark, director of trading, Nollenberger Capital Partners, told the WSJ. "It's kind of unsettling." Without any disclosure requirements, we have no idea who those somebodies are, much less the amount of their holdings. That creates additional uncertainty, which is about the last thing the markets need.