Seriously, what is with the saliva chemical test I wonder? There's gotta be a very solid explanation. My guess is that non-fog saliva reacts with fog-mutated food, and fog-mutated saliva reacts with non-fog food. In which case, is the fog some type of nanobot swarm, or is it your generic handwavium super-disease/parasite from another dimension? It seems biological in nature from what we've seen so far with the gate/portal thing and the "bears".