Internet boffins have hacked the PC Left 4 Dead demo to allow players to control the Infected, or zombies as we call them.
There's a step-by-step guide on the Steam forum, plus a reminder that this is an unsupported feature and so has plenty of bugs and balance issues.
But if you're feeling adventurous, why stop there? Another clever clogs has cobbled together some code to allow split-screen multiplayer in the demo. This involves having an Xbox 360 controller lying around and editing some .cfg files.
Finally, there's a chap who's got user maps working in the sampler, somehow. There's a video of the map in question, plus the usual waiver of slightly raw and unsupported content.
The Left 4 Dead demos will be released to the public tomorrow on PC and Xbox 360. However, those pre-ordering the game from Steam have had access since last Thursday.
The full PC version launches on Steam from 18th November, while retailers will stock Xbox 360 and PC boxes from 21st November.
Head over to our Left 4 Dead gamepage to catch up.