The MiM started early neutral and as I checked in during the closing hours you could see a steady build to the sell-side. That build caught the attention of the market around 3:30 pm and there was a steady 20 minutes of selling set up. At the 3:50 pm reveal, when it all becomes real, a 1.3B sell imbalance had already been sold off.
The HFTAlerts monitor picked up a sizeable count of program trades, 47. They were mostly to the sell-side with only 13 buy programs and 34 sells.