In other species, it's entirely in overdrive, which means they're sounding an alarm and releasing molecules to stop a virus from replicating before it even enters their body.
Thing is, the indie scene doesn't have a great track record when it comes to sales, and whenever something does sell, a segment of the community tends to go into clone overdrive. Just look at the App Store.
Whatever the cause is, in response the coagulation pathway goes into overdrive, resulting in widespread clot formation which plugs up medium and small blood vessels which leads to ischemia, necrosis, and eventually organ damage.
It's possible that evolution is actually working on overdrive here near the equator, the speciation, the creation of new species by various natural forces, actually happens faster near the equator.
But the switches in any one cell aren't set in stone: teaching those rats to fear that fruity smell switched one of their smell-sensing genes into overdrive.
This causes the immune system to go into overdrive and destroys your gums and ligaments, resulting in advanced Periodontitis where your teeth become loose and begin to fall out.
So basically, our brain's threat detection system, the amygdala, it kicks into overdrive whenever we perceive something as scary or uncertain, even if there's no real danger.