Summary: injured marines can be found anywhere, as if they had been parasited.

Observation: "You wouldn't know it to look at us, but after the archive collapse we were hurting, especially Nem. We just needed to get back to the elevator and wait for some resources to trickle in, but they kept the pressure on, every step of the way. We put Nem in the middle, they attacked the middle; we put him in back, they attacked the back. It only took a few spikes to finish him off: a Lerk shattered a window and nailed him before we could cover. Hit-and-run bastards. Then they started stalkin' Hanover. I'm telling you: they knew who was hurtin', and they were picking us off, one at a time."

Thesis: the most efficient ambush targets the weakest prey. Or: the best way to attack many foes is to reduce their number as quickly as possible. Injured humans release microscopic triggers when injured or harmed – these aliens must be alert to these emissions, evolving skin receptors that can "taste" the air and pinpoint injured foes. TSA armor should suppress tell-tales like these – the aliens must be amazingly sensitive. Or perhaps the ever-present bacterial network is responsible. This evolution is probably susceptible to all kinds of tricks, or evasions – but our experiments with "scent bombs" proved disastrous. As is the case with all aspects of the Kharaa, we need more data … but what is an acceptable number of deaths for each bit of information? For now, we must be satisfied with observation, and observation only.