A bullet allows you to short a stock on a downtick.It consists of a long stock and long deep in the money put position.It expires at the end of the day.
the final words http://www.elitetrader.com/vb/showthread.php?s=&postid=96308&highlight=bullet#post96308 go to top right hand corner, click search then enter author name or words, you should be able to get wealth of information