Dr Kessler's research largely contradicts what Dr West says in the first game. The immune are told by Dr West (in reference to the virus) "It doesn't mutate, it doesn't replicate, it just dies." While Dr Kessler tells them a different story in that the virus is not dead, but simply dormant, and could possibly mutate if exposed to certain mutagenic chemicals.
Luggage can be found in the old Japanese tunnels.
The zombies are infected with a virus and are not actually dead, yet the heat sensor at the military base is not set off by them.
Frank Serpo replies too quickly about the plan to put fuel on the bulldozer.
As you progress in Henderson, some female zombies will sound like male zombies, and some male zombies will sound like the female zombies.
Dead bodies that haven't turned into zombies make the same noise when striking the body as zombies do when hit.
South American birdsong on a Pacific island.
The rank of lieutenant colonel is pronounced the American way by an Australian.
NPCs may complain about the noise the pump will make after it has been turned on.