At the Penny Arcade Expo out here in Seattle, Valve Software is showing some Portal 2 co-op in action. I got to see four basic levels from what appeared to be the start of the co-op campaign. Introducing: the ping.

The co-op campaign is a standalone adventure that will be double the length of Portal 1. It's part of Portal 2, which is coming out in February on PC, Mac, PS3 and Xbox 360. In co-op, two players can link up via the Internet, split-screen or through a local connection. Each controls a test robot, and each robot will be armed with a portal gun that can shoot two portals. As they did in Portal 1, the portal guns fire an entry and an exit portal. You need to use the portals to get out of the locked rooms and deathtraps you keep finding yourselves in. Because there are two players and two guns, co-op players will be able to create a total of four portals, but player 1's portals will be linked only to each other, player 2's to just his or her own.

In the PAX theater, we got to see two players each using their own TV. I shot video of one TV at a time, switching back a couple of times. Hopefully I didn't make it too confusing!

Here's the first trial we were shown, which armed the players with their portal guns and introduced the ping tool, which lets players mark places where they want their buddy to fire a portal.

In the second trial, we were introduced to the reflective cube. You'll also see throughout these videos that there's a gesture system. You can make nice with your co-op buddy, when you're not reflecting lasers into each other.

The third trial introduces the hard light bridge, which, well, is cool. Watch:

The fourth trial brings back Portal 1's great infinite jump. And, if you've watched all,you'll have heard some great lines from GLaDOS. She's got jokes for the co-op players too.