How does a cat use its whiskers?

The usual answer is that the whiskers are feelers that enable a cat to tell whether a gap is wide enough for it to squeeze through, but the truth is more complicated and more remarkable. In addition to their obvious role as feelers sensitive to touch, the whiskers also operate as air-current detectors. As the cat moves along in the dark it needs to manoeuvre past solid objects without touching them. Each solid object it approaches causes slight eddies in the air, minute disturbances in the currents of air movement, and the cat's whiskers are so amazingly sensitive that they can read these air changes and respond to the presence of solid obstacles even without touching them.

The whiskers are especially important – indeed vital – when the cat hunts at night. We know this from the following observations: a cat with perfect whiskers can kill cleanly both in the light and in the dark. A cat with damaged whiskers can kill cleanly only in the light; in the dark it misjudges its killing-bite and plunges its teeth into the wrong part of the prey's body. This means that in the dark, where accurate vision is impeded, healthy whiskers are capable of acting as a highly sensitive guidance system. They have an astonishing, split-second ability to check the body outline of the victim and direct the cat's bite to the nape of the unfortunate animal's neck. Somehow the tips of the whiskers must read off the details of the shape of the prey, like a blind man reading braille, and in an instant tell the cat how to react.

Photographs of cats carrying mice in their jaws after catching them reveal that the whiskers are almost wrapped around the rodent's body, continuing to transmit information about the slightest movement, should the prey still be alive. Since the cat is by nature predominantly a nocturnal hunter, its whiskers are clearly crucial to its survival.

Anatomically the whiskers are greatly enlarged and stiffened hairs more than twice the thickness of ordinary hairs. They are embedded in the tissue of the cat's upper lip to a depth three times that of other hairs, and they are supplied with a mass of nerve-endings which transmit the information about any contact they make or any changes in airpressure. On average the cat has twenty-four whiskers, twelve on each side of the nose, arranged in four horizontal rows. They are capable of moving both forwards, when the cat is inquisitive, threatening, or testing something, and backwards, when it is defensive or deliberately avoiding touching something. The top two rows can be moved independently of the bottom two, and the strongest whiskers are in rows two and three.

Technically whiskers are called vibrissae and the cat has a number of these reinforced hairs on other parts of its body – a few on the cheeks, over the eyes, on the chin and, surprisingly, at the backs of the front legs. All are sensitive detectors of movement, but it is the excessively long whiskers that are by far the most important vibrissae, and it is entirely apt that when we say that something is 'the cat's whiskers' we mean that it is rather special.