Tip of a cat's whisker, coloured scanning electron micrograph (SEM). A cat's whisker, also known as a vibrissa, is a sensory tool. Whiskers are long stiff hairs made of the fibrous protein keratin. At the root of each of these hairs is a follicle loaded with nerves. By brushing their whiskers against an object a cat is able to detect the precise location, size and texture of the object which is especially useful when in the dark. The whiskers can also detect changes in the air current which can alert cats to approaching danger. Magnification: x800 when printed at 10cm wide.