Rats are various medium sized rodents. "True rats" are members of the genus Rattus, the most important of which to humans are the black rat, Rattus rattus, and the brown rat, R. norvegicus. Many members of other rodent genera and families are also called rats and share many characteristics with true rats. A rat has an average life span of 2-3 years[1].

Rats are distinguished from mice by their size; rats generally have bodies longer than 12 cm (5 in).
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* 1 Species and description * 2 As pets * 3 As subjects of scientific research * 4 Laughter in rats * 5 As food * 6 In culture o 6.1 In Eastern cultures o 6.2 In Western cultures o 6.3 In religion
Stem cells from humans can be removed from the recipient of the donated organ, thereby eliminating rejection by the immune system. The resultant transplanted bioartificial organ will benefit many heart patients.[3]

Domestic rats differ from wild rats in many ways. They are calmer and less likely to bite; they can tolerate greater crowding; they breed earlier and produce more offspring; and their brains, livers, kidneys, adrenal glands, and hearts are smaller (Barnett 2002).

Brown rats are often used model organisms for scientific research. When conducting genetic research rats are much rarer than mice. When it comes to conducting tests related to intelligence, learning, and drug abuse, rats are a popular choice due to their high intelligence, ingenuity, aggressiveness, and adaptability. Their psychology, in many ways, seems to be similar to humans. Entirely new breeds or "lines" of brown rats like the Wistar rat have been bred for use in laboratories. Much of the genome of Rattus norvegicus has been sequenced.[4]

[edit] Laughter in rats
Brown Rat (Rattus norvegicus)
Brown Rat (Rattus norvegicus)

It was discovered that rats emit short, high frequency, ultrasonic, socially induced vocalization during rough and tumble play, and when tickled. The vocalization is described as a distinct "chirping." Humans cannot hear the "chirping" without special equipment. It was also discovered that, like humans, rats have "tickle skin": certain