Here's a trick for those rompin' and stompin' with zombies this Christmas: A physics glitch that enables you to charge up a gatling gun and launch yourself across the map in Left 4 Dead.
Basically, wham on the gun like Engineer fast-building a sentry gun in Team Fortress 2, and when you think you've hit it enough, jump aboard and it'll launch you in the direction it is aimed. The distance seems to correlate to the amount of whams. In the second attempt, that guy pumps it up like a kid overcharging his Red Ryder dawg-plunker and sails clean over the crescendo point. Looks useful, or fun. Or both. Or neither.
Left 4 Dead Glitch - Gatling Launch [YouTube]