In an unexpected cross-promotion, late-night cable network Adult Swim are teaming up with Valve for a mysterious promotion. On the just-launched official page for the project, it simply states:

ADULT SWIM AND VALVE ARE TEAMING UP FOR SOMETHING THAT YOU'LL PROBABLY ENJOY. TO LEARN HOW THEIR VIDEO GAME PEANUT BUTTER WILL BE GETTING IN OUR NETWORK'S CHOCOLATE, COME BACK NEXT WEEK.  ALSO: YOU'LL WANT TO SIGN UP FOR THE NEWSLETTER. YOU'VE BEEN WARNED.

Based on the Team Fortress 2 image, odds are this will have something to do with an ARG, much like Valve's Potato Sack game last year.

Head over to the project's page to register for the newsletter. As Adult Swim states, "You've been warned.".