Greetings everyone, I've been trading for a few months and in an attempt to expand my toolbox I've been watching level 2 quotes. I am sure everyone heard about DNDN dropping 50% in a few seconds. A similar thing happened to CELG today (not to the extent, of course.) If you look at the chart and the corresponding L2 quotes you will notice a sudden and unexplained drop of almost $.5 in 2 seconds. I've been watching the stock for a number of days and it has been trading very steadily. The prices are outside the bid/ask spread. I realize that more than 100,000 shares changes hands in a few seconds, but would like to know the mechanism. No news or related events took place. Response from anyone with the knowledge would be greatly appreciated. Thank you