Have been told it is listing for unusual noises, for instance, most animals only expel tiny amounts of air where a human much more ait so sitting still you can hear a human breath from a considerable distance. Aroma everything has a smell the modules in the air can be an indication of something near that is prey or predator depending on how you look at it. Vibrations certain material relay mild vibrations can be a warning sign. This is a reason to learn foot placement most not all people walk heavy they never even realize it.

@azzow2 medically, that’s not the part we referenced so I can’t confirm that, just the link to hind brain activities that are base survival.

Never looked it up had heard it in the service.

@JustKip. Pretty cool...