A chain of associations led me to the kafers in the role-playing game (Traveller) 2300 AD. I played it a few times in the eighties, and one of the things I remember was that the Kafers had an ability to disappear. They attacked, we opened fire, they disappeared. This was some secret ability they had, but I never played long enough to figure it out. Now, twenty years later, to save me some sleep, could somebody tell me how they did it?
The Kafers’ schtik was that their equivalent of adrenalin didn’t make them stronger or faster, it made them smarter. Militarily, it means that about 30 seconds after the shooting starts the Kafers go from “clueless redneck” to “special forces” - at which point they take cover, then set about reversing the ambush on whoever’s attacking them. Psychologically, it means that the Kafers are violence junkies - violent and stressful situations are the only time they’re fully sentient.