The hyper-short co-op trailer for Portal 2 posted below paints an idyllic picture of how the game's multiplayer component should function: With two robots working together to solve a common goal. It does not show what will actually happen when we and our poor, unassuming friends get our hands on the game, which is to say, two robots bending the laws of physics and gravity in an attempt to murder each other in the most clever manner imaginable.

So, for a good example of Portal 2 co-op, watch the video below. For a bad example, wait for the game to come out, play it with us, and get gravitymurdered.