Oct, mine had sound (got it from FilePlanet).
And yes... the physics are insane. What your missing without sound is the managing director (of Valve I think... maybe Sierra) explaining whats happing.
The few minutes are obviously to show off the Source engine. Some really mpressive stuff - the "deformable environment" that people have been claiming is in their product for years ACTUALLY is this time around!
The textures, camera, deformable terrain, water effects, and the fact that everything behaves exactly like its real life counterpart is amazing. Shoot a piece of wood, it breaks, some flies into the water, it floats. Shoot a barrel, it rolls, falls into the water and sinks.
Anyway - there are some great "techie" wizecracks from people in the background during the footage (which is taken from E3). At some point, when the guy is explaing the engine, and showing the mattress, wood, and barrels near the "pool" some guy opens up and says "And this will run on my 486?" Even I snickered at that one.
