In Last of the Annamese, I write of tingle at the base of the spine that the protagonist, Chuck Griffin, feels when danger is near. The idea came from my own experience.
I became consciously aware of the sensation early in my years in Vietnam. I felt it in moments of peril. It only occurred when my conscious mind was unaware of the menace. As soon as I noticed it, I turned my attention to looking for proximate hazards. The warning was nearly always accurate.
I have often wondered at it. It reminds me of artistic inspiration in the sense that it feels as though it originates outside of me, as if another, unseen being were communicating with me. I can understand why the ancient Greeks, among others, believed in muses and other spirits that intervened in daily life to inspire, warn, or enlighten.
The tingle inspires in me utmost respect for the human subconscious. I see that so much in my life originates in that dark place in my soul that is hidden from waking mind. In me and all human beings there is wisdom and knowledge and beauty waiting to spring into consciousness. The trick is to learn to release the underlying spirit and use its bounty.