Since Bungie and Microsoft started letting people mess around with Halo 3, the companies have continued to tease the supposed function of the X button on the controller. We know it's not sprinting, so what is it? Does it enable the shield hinted at in last year's teaser commercial? Can you quickly enable team-speak? Right now, Bungie isn't saying diddly about it, but we should know soon enough -- it'll be in the beta.