Says the hunter Jim Corbett, in Man-Eaters of Kumaon:
I have made mention elsewhere of the sense that warns us of impending danger, and will not labour the subject further beyond stating that this sense is a very real one and that I do not know, and therefore cannot explain, what brings it into operation. On this occasion I had neither heard nor seen the tigress, nor had I received any indication from bird or beast of her presence and yet I knew, without any shadow of doubt, that she was lying up for me among the rocks.
And again:
The premonition of impending danger is too well known and established a fact to need any comment. For three or four minutes I had stood perfectly still with no thought of danger and then all at once I became aware that the tiger was looking at me at a very short range. The same sense that had conveyed the feeling of impending danger to me had evidently operated in the same way on the tiger and awakened him from his sleep.
Now it’s mountaineer Joe Simpson, in Touching the Void:
As I climbed up to rejoin his tracks it occurred to me that I had felt a moment of anxiety only minutes before Simon had fallen. I had noticed this in the past and always wondered about it. There had been no good reason for the sudden stab of worry.
And again:
I wanted to sleep. I couldn’t be bothered to move any more. I was warm enough sleeping on the snow. The storm would cover me like a husky and keep me warm. I nearly slept, dozing fitfully, edging close to the dark comfort of sleep, but the wind kept waking me. I tried to ignore the voice, which urged me to move, but couldn’t because the other voices had gone. I couldn’t lose the voice in daydreams. ‘…don’t sleep, don’t sleep, not here. Keep going. Find a slope and dig a snow hole… don’t sleep.’
Once experienced, the reality of such a feeling is put beyond question. And it would be no exaggeration to say that adventurers like those mentioned above depend on it and trust it. The examples could go on and on… In extreme situations, for some reason, something happens. Whether the perception of danger is dependent on total absorption in the environment, cannot be said. But something happens, and perception screams out even without the support of the “traditional” senses. In many ways, man is far more interesting and complex than is often assumed…