I was thinking about how to reward killing zombies. Right now, zombies are more a nuisance than anything. I don't really get anything for killing them, and they are almost trivially easy to escape. Part of this is just difficulty tweaking. I want to be scared of zombies again. But also, zombies are too predictable.. I know that if I am in the wilderness, I'm relatively safe, and if I'm in a city, I need to listen for zombies shouting at me. Instead, maybe the game can use something like the grid squares in the insurgency mission. There are hot and cool squares. Only hot squares spawn zombies. A certain number of squares start hot at the beginning of the game. Say, every square of city, like the zombie spawn pattern now. Then, as zombies wander, they can turn other squares hot. But, on the other hand, if every existing zombie in a square is killed, then the square is now cool, and does not spawn zombies until an existing zombie wanders in to turn it hot again. Obviously, to keep from having to simulate zombies with no players nearby, there would also have to be a heuristic for the spread of hot squares that is computationally simple. This would also mean that zombies can realistically wander into the countryside. I feel this would add a new dimension to the game. That is, there is a reward for killing zombies above and beyond just surviving an attack. Now you can potentially create "safe" spaces. To keep things from being totally safe, which would be boring, there could be a small chance for a cool square to spontaneously turn hot. This chance could increase, the larger the contiguous cool area surrounding that square, so that it wouldn't be realistic to expect to establish and defend an entire city, but maybe it would be possible to clean out a village or an apartment complex.