We've got the zombies. Where's the plants?
Valve's tipped its hat to another title which features the living dead in the form of PopCap's Plants vs Zombies in The Passing for Left 4 Dead 2.
In one of the safe houses for the shooter, a scribbled message is seen on the wall from someone called Crazy Dave, who so happens to be your neighbour in the tower-defense game, stating:
"Looking for an M60? Come see me - Crazy Dave."
It was discovered over the weekend that the game also nodded a reference to Capcom's Dead Rising with a message from main character Frank West.
More of these in future please, Valve.