All hairs are associated with muscles, and most have a muscle called the erector pili, which serves to move the hair from its normal inclined position to a more erect position. In the case of the vellus hairs of man this produces what is commonly called goose bumps. This muscle is in a position to help squeeze oil from the sebaceous glands, which are also attached to the hair follicle. Erector pili muscles are supplied with nerves of the sympathetic nervous system, which is often associated with our response to flight and fright stimuli. Thus, when we are frightened we may get goose bumps. We also get goose bumps when we are chilled. Contraction of the erector pili muscles produces heat, and if this response is inadequate to warm the body, shivering may follow, which involves repeated contractions of the large body muscles.