SIM:
19.00 is the lowest point and has been tested 4 time during the last 10 days (from 2006-12-01 to 2006-12-13).

Today, 19.00 was retested again.
when 19.00 was first hit, a huge buy order came in (bid x ask = 136:2),
when prices moves to 19.01, bid x ask = 2x2.
obviously, some one has placed a large limit buy order at 19.00.

However, when the price came down again one minutes later, the buy order is gone!!!!
Then, disaster happened, the price dropped almost 1 dollor in 1 or 2 minutes.
then bounce back to 18.60, this should be the second good time to short, then the price went down to 17.20 during the next 2 or 3 hours.

I think this is a classic example.