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The animal on the cover of JavaScript: The Definitive Guide, Fifth Edition, is a Javan rhinoceros. All five species of rhinoceros are distinguished by their large size, thick armor-like skin, three-toed feet, and single or double snout horn. The Javan rhinoceros, along with the Sumatran rhinoceros, is one of two forest-dwelling species. The Javan rhinoceros is similar in appearance to the Indian rhinoceros, but smaller and with certain distinguishing characteristics (primarily skin texture).
Rhinoceroses are often depicted standing up to their snouts in water or mud. In fact, they can frequently be found just like that. When not resting in a river, rhinos will dig deep pits in which to wallow. Both of these resting places provide a couple of advantages. First, they give the animal relief from the tropical heat and protection from blood-sucking flies. (The mud that the wallow leaves on the skin of the rhinoceros provides some protection from flies, also.) Second, mud wallows and river water help support the considerable weight of these huge animals, thereby relieving the strain on their legs and backs.