Piloerection: Erection of hair. Why does man get goosebumps? This holdover from ancient man supposedly made it possible for our hairs to plump up and create better insulation. When we feel threatened, it can happen as well, which can easily be seen in cats and dogs when their coats rise. This allows for looking bigger and more threatening. We also get them during emotional moments.
I was talking to someone recently who had several encounters with Bigfoot and one of them was quite impressive in which he saw that the Bigfoot's hair was standing on end. Whether it felt scared, threatened, or whatever, it would seem to be indicative of a primitive man/modern man type of reaction. This hair-standing-on-end reaction is also found in chimps.
Interestingly, "Goosebumps may be proof that humans descended from much hairier people or apes. It could be that in future generations as the body becomes more efficient, the ability to have goosebumps may be lost." "People get goosebumps also when they are frightened, no matter how hot it is. This may be an attempt to make us look larger by having out hair bristle."
In Jane Goodall’s description “Male chimpanzees show their power in “displays.” Their hair stands on end so they look bigger, they scream, stamp their feet, and go on a tear, dragging branches, or hurling rocks. This may scare other chimpanzees and keep them from picking a fight.” Therefore I think other than fear and cold, anger or aggressivity is another reason to stand your hairs on end!
Given this information, should one come across a Bigfoot and see his hair stand on end, some assumptions can be made about his state of mind, feeling scared or threatened. I'd suggest to the human that encounters him, look down and don't engage him into feeling he must confront you. Best, to lower your head and back away. One thing we know is that Bigfoots do not want to run into humans and they certainly don't want confrontation, so consider that signal a silent blessing because your goosebumps are going to do nothing to intimidate him.