<P> As a response to cold: in animals covered with fur or hair, the erect hairs trap air to create a layer of insulation . Goose bumps can also be a response to anger or fear: the erect hairs make the animal appear larger, in order to intimidate enemies . This can be observed in the intimidation displays of chimpanzees, some New World monkeys like the cotton - top tamarin, in stressed mice and rats, and in frightened cats . In humans, it can even extend to piloerection as a reaction to hearing nails scratch on a chalkboard, listening to awe - inspiring music, or feeling or remembering strong and positive emotions (e.g., after winning a sports event, or while watching a horror film). Moreover, there are rare accounts of people who are able to deliberately evoke goose bumps in themselves without any external trigger . Such people tend to have the ability to increase their heart rate and describe the event as a chill from the base of their skull down the body, that causes the increase in heart rate and concurrent goosebumps on the skin especially the forearms which varies in duration . Further research is needed to discover more on such people . Goose bumps are accompanied by a specific physiological response pattern that is thought to indicate the emotional state of being moved . </P> <P> In humans, goose bumps are strongest on the forearms, but also occur on the legs, neck, and other areas of the skin that have hair . In some people, they even occur in the face or on the head . </P> <P> Piloerection is also a classic symptom of some diseases, such as temporal lobe epilepsy, some brain tumors, and autonomic hyperreflexia . Goose bumps can also be caused by withdrawal from opiates such as heroin . A skin condition that mimics goose bumps in appearance is keratosis pilaris . </P> <P> Goose bumps can be experienced in the presence of flash - cold temperatures; for example, being in a cold environment, and the skin being able to re-balance its surface temperature quickly . The stimulus of cold surroundings causes the tiny muscles attached to each hair follicle to contract . This contraction causes the hair strands to stand straight; the purpose of which, is to aid in quicker drying, via evaporation of water clinging to the hair, which is moved upward and away from the skin . </P>

Which of the following pulls the hair upright during fright or cold situations