I place a limit order, which I guess you could see if the depth were deep enough, but I could very well have programmed an algorithm to just monitor the prices and do market orders instead, which you definitely wouldn't see. I'm sure most traders do it that way.
The interesting thing is that on the day of the Flash Crash, if I'm not mistaken the ES futures contract bounced exactly off the 200 day MA. So, one thing that the flash crash revealed is a lot of algorithms programmed into the markets that would normally never have been revealed. So if you want, keep a floating order just above the 200 day and you might make a few dozen points in a few mins, just like May 6, 2010!
The interesting thing is that on the day of the Flash Crash, if I'm not mistaken the ES futures contract bounced exactly off the 200 day MA. So, one thing that the flash crash revealed is a lot of algorithms programmed into the markets that would normally never have been revealed. So if you want, keep a floating order just above the 200 day and you might make a few dozen points in a few mins, just like May 6, 2010!