Ok ok. One more.

TheStreet/com:  NEW YORK (TheStreet) -- The unusual trading action in Procter & Gamble(PG) stock believed to be at the center of the market's most volatile moments on Thursday is thought to have originated from Terra Nova Financial(TNFG), a Chicago-based provider of prime brokerage and clearing services, a person familiar with the situation has told TheStreet...Terra Nova has broker-dealer status with both the Securities and Exchange Commission and the Financial Industry Regulatory Authority, or FINRA. One of the services it offers is sponsored direct market access, which it says allows clients to "establish a direct connection between their proprietary platforms and the Nasdaq or NYSE Arca execution systems," so the trade -- characterized as a large sell order in P&G -- could have come from one of the firm's clients with this type of access. ...Terra Nova's customers appear to be mostly hedge funds, but it also provides clearing services for other broker-dealers and registered investmentadvisers.

The SEC is already moving toward clamping down on sponsored direct market access, which is often referred to as "naked" or "unfiltered" access, having proposed a new rule to effectively prohibit it back in January...

The scenario outlined for TheStreet is that, shortly after the P&G sell order came through to the NYSE, the machines took over. An initial trade of P&G down to the $56 range is believed to have been filled at the NYSE before a mechanism designed by the exchange to react to sudden volatility in a stock price slowed down trading and brought human specialists into the mix.

In the meantime, the rest of the sell order was simultaneously spiraling out electronically to other trading venues in accordance with the National Market System's trade-through rule that makes all bids and offers for stocks listed on various exchanges visible to all market makers. At that point, stop limits and program trading kicked in, and the subsequent selling pressure overwhelmed pricing in not only P&G but other issues, including many ETFs, as trading algorithms reacted to the move in P&G.