i noticed that some times therer will be a big change in the spreads in the Time and Sale window.. For example, the screen will show upticks or downticks or spread that are very narrow, and all of a sudden, out of nowhere, a big spread pops up. so, what exactly is the meaning of and purpose behind this? what is the specialist trying to do here? slow down the market a little bit so he can catch a breath or something? and what does it mean when a stock you're trayind all of a sudden halts and displays a bid and offer price of 0, then quickly resume the trades within a couple of seconds.