Piloerection, noun (pi·lo·erec·tion): “bristling of hairs due to the involuntary contraction of small muscles at the base of hair follicles that occurs as a reflexive response of the sympathetic nervous system especially to cold, shock, or fright”
For humans, we are familiar with piloerection as goosebumps or when the hair on the back of our neck stands up. Since chimpanzees have longer, thicker hair that covers their entire bodies, we can really notice when their arousal levels change.
Here is Jamie working up to a display. In addition to grabbing her barrel so she can bang her fists on it and push it around, her hair starts to stand on end to make herself look bigger (and more intimidating):