Anyway, the game's got some issues due to its physics engine -- the most notable issue is in the Versus mode where it's possibly for enemy zombies to intentionally block paths, making it impossible for the zombie survivors to move forward. It's an exploit, and beyond that it's a stupid thing to do.
So today I had the great fortune of joining a team that was blocking the sewer hole on No Mercy 2 like a buncha douches... except, just as I was about to leave, I spawned as the car-throwing Tank right next to my exploiting team-mates.
I'll let you figure out what happened next. >:)