The word squirrel, first attested in 1327, comes via Anglo-Norman esquirel from the Old French escurel, the reflex of a Latin word sciurus which was itself borrowed from Greek. The word itself comes from the Greek word σκίουρος, skiouros, which means shadow-tailed, referring to the bushy appendage possessed by many of its members.

The native Old English word, ‘ācweorna’, survived only into Middle English (as aquerna) before being replaced.[1] The Old English word is of Common Germanic origin, with cognates such as German Eichhorn/Eichhörnchen and Norwegian ekorn.

Squirrels are generally small animals, ranging in size from the African pygmy squirrel, at 7–10 cm (2.8–3.9 in) in length, and just 10 g (0.35 oz) in weight, to the Alpine marmot, which is 53–73 cm (21–29 in) long, and weighs from 5 to 8 kg (11 to 18 lb). Squirrels typically have slender bodies with bushy tails and large eyes. Their fur is generally soft and silky, although much thicker in some species than others. The color of squirrels is highly variable between – and often even within – species.

The hindlimbs are generally longer than the forelimbs, and they have four or five toes on each foot. Their paws on their forefeet include a thumb, although this is often poorly developed. The feet also have a soft pad on the underside.

Squirrels live in almost every habitat from tropical rainforest to semiarid desert, avoiding only the high polar regions and the driest of deserts. They are predominantly herbivorous, subsisting on seeds and nuts, but many will eat insects, and even small vertebrates.

As their large eyes indicate, squirrels generally have an excellent sense of vision, which is especially important for tree-dwelling species. They also have very versatile and sturdy claws for grasping and climbing.[4] Many also have a good sense of touch, with vibrissae on their heads and limbs.

source

The cat (Felis catus), also known as the domestic cat or housecat to distinguish it from other felines and felids, is a small domesticated carnivorous mammal that is valued by humans for its companionship and ability to hunt vermin and household pests. Cats have been associated with humans for at least 9,500 years, and are currently the most popular pet in the world. Owing to their close association with humans, cats are now found almost everywhere on Earth.

Their adaptability, rapid breeding rate, and predatory instincts make them effective hunters. In some locations, cats have affected indigenous animal populations; this has led them to be classified as an invasive species in some areas. Many problems are caused by the large number of feral cats worldwide, with a population of up to 60 million of these animals in the United States alone. Failure to control the breeding of pet cats by spaying and neutering and the abandonment of former household pets cause the development of such feral colonies.

Cats are similar in anatomy to the other felids, with strong, flexible bodies, quick reflexes, sharp retractable claws, and teeth adapted to killing small prey. As nocturnal predators, cats use their acute hearing and ability to see in near darkness to locate prey. Not only can cats hear sounds too faint for human ears, they can also hear sounds higher in frequency than humans can perceive. This is because cats’ usual prey (particularly rodents such as mice) make high frequency noises, so cats’ hearing has evolved to pinpoint these faint high-pitched sounds. Cats rely more on smell than taste, and have a vastly better sense of smell than humans.

source