A new trailer from Portal 2 offers the third in a series of four investor presentations from Valve's upcoming first-person puzzle game sequel. In this clip Aperture CEO Cave Johnson introduces turrets, which he calls the consumer version of their most popular military-grade product. The clip shows just how they get so many bullets into each turret, how the turret fires 65% more bullet per bullet, the variety of colors they come in, and the practical home uses of such a product. The embedded clip follows.