Characters: Advanced facial animation system delivers the most sophisticated in-game characters ever seen. With 40 distinct facial "muscles," human characters convey the full array of human emotion, and respond to the player with fluidity and intelligence. Physics: From pebbles to water to 2-ton trucks respond as expected, as they obey the laws of mass, friction, gravity, and buoyancy. Graphics: Source's shader-based renderer, like the one used at Pixar to create movies such as Toy Story® and Monster's, Inc.®, creates the most beautiful and realistic environments ever seen in a video game. AI: Neither friends nor enemies charge blindly into the fray. They can assess threats, navigate tricky terrain, and fashion weapons from whatever is at hand.