by ligaments, like humans. This contributes to the cat's elasticity and ability to elongate and contract their back by curving it upwards or oscillating it along their vertebral line. Cats are also able to jump from greater heights without serious injury, due to the efficient performance in their limbs and ability to control impact forces. In this case, hindlimbs are able to absorb more shock and energy in comparison to the forelimbs, when jumping from surface to surface, as well as steer the cat for weight bearing and breaking. Claws Like nearly all members of the family Felidae, cats have protractable claws. In their normal, relaxed position, the claws are sheathed with the skin and fur around the toe pads. This keeps the claws sharp by preventing wear from contact with the ground and allows the silent stalking of prey. The claws on the forefeet are typically sharper than those on the hind feet. Cats can voluntarily extend their claws on one or more paws. They may extend their claws in hunting or self-defense, climbing, "kneading", or for extra traction on soft surfaces (bedspreads, thick rugs, skin, etc.). It is also possible to make a cooperative cat extend its claws by carefully pressing both the top and bottom of the paw. The curved claws can become entangled in carpet or thick fabric, which can cause injury if the cat is unable to free itself. Most cats have a total of 18 digits and claws. 5 on each forefoot, the 1st digit being the dewclaw; and 4 on each hind foot. The dewclaw is located high on the foreleg, is not in contact with the ground and is non-weight bearing. Some cats can have more than 18 digits, due to a common mutation called polydactyly or polydactylism, which can result in five to seven toes per paw. Temperature and heart rate The normal body temperature of a cat is between . A cat is considered febrile (hyperthermic) if it has a temperature of or greater, or hypothermic if less than . For comparison, humans have an average body temperature of about . A domestic cat's normal heart rate ranges from 140 to 220 beats per minute (bpm), and is largely dependent on how excited the cat is. For a cat at rest, the average heart rate usually is between 150 and 180 bpm, more than twice that of a human, which