Are small rodents living with human beings and are popular because of the damage they cause to crops, stored food and even clothes. Humans enjoy them as pets and scientists use them for clinical and scientific testing. Their body length varies from 7.5 to 10 cm while the tail adds another five to ten cm. They weigh around 10 to 25 grams and have been found in a variety of fur colors including white, grey, brown and black. They can jump vertically to about 45 cms, have strong smell and a high pitched squeak. Interestingly, they use all four legs for walking and running, but in case they attack someone or are trying to eat, they stand up on the two hind legs and use the tail as a third supporting arm. Using the two free arms, they hold their food and eat. They are also good swimmers and climbers and are usually seen during the night hours. They like eating plants but are omnivorous in nature. They cannot see colors but are able to hear the ultrasonic sounds and use both human audible range and ultrasonic range for communication.