I just remembered this part of The Animal Dialogues:
"In the last hour of dawn, I woke from a long nap in the sand. I crawled from my sleeping bag, which I had pulled out when we all dropped our water weight sometime in the night. Our camp looked like abandoned debris in the middle of a rippled, tawny-colored dune field. A void encircled me, occupying every horizon. There was no wind, only a still and pale sky. I got up and stepped barefoot across sand as fine as table salt. Not three feet away, I stopped at a fresh track left by a sidewinder. I followed it with my eyes back toward my gear, finding that while I slept a snake had passed beside my head. It had left a graceful, rhythmic print, something written in script."
OK, this is not as frightening as the time Craig Childs walked out of his tent in the Arctic to find a grizzly sitting there, and yet, it gives me the shudders all the same.