That theory does make sense. Although I wonder how it could be proven.
This particular snake was shading itself under a bush. The temperature was probably in the high 80's F. So its metabalism was not optimal. He did not want to be moved, but I used my hiking staff to get him off the trail, otherwise my wife was NOT going forward. :)
I am embarassed to note, that on our return trip an hour later, he had returned to the same spot, and I did not see him AGAIN. But my wife sure did. And I moved him for the 2nd time.
I live in the desert, but see many more snakes at 5,000' - 7,000' where food is more readily available. Normally it seems that snakes found on/near the trail happen when it is warmer, which could explain why no warning rattle. It seems that every time I hear a rattle, I can't see the snake, and it is far enough away, not to worry about it. Those non-warning snakes on the trail are difficult to move, because they just seem lethargic.