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This article contains information relating to a hoax. According to Cambridge dictionary a hoax is "a plan to deceive a large group of people; a trick."
In mythology, a Unicorn is simply an animal (most commonly seen is the horse) with a single horn. This single horn is supposed to be on the mid line of the body, such as the centre of the forehead, and it needs to have grown there naturally. Nearly everyone agrees that a two-horned animal with one horn that broke off or failed to grow is not a unicorn.
Beyond this fact, it is hard to define a unicorn. A multitude of different unicorn species populated the mythology of nations in Europe, Asia and Africa. The original unicorn seems to be the one spoken of in myths from India. It was often thought to live in inaccessible, mountainous terrain such as the mountains of Tibet. This animal seemed like a wild ass or antelope with one horn. The unicorn of China combined body parts from several animals and was perhaps the smallest unicorn. Its horn was short, soft and harmless.
Because of its single nose horn, the rhinoceros was often called a unicorn, technically, it fits the requirement of having a single, natural, centered horn, but it does not look like the general type of unicorn that the largest number of myths have focused on. Despite this, the rhinoceros is often trotted out as an all-purpose explanation for all unicorn sightings, including those in Europe, where Medieval peasants would not have had a chance to see any such creature. (Note: Ancient and Medieval Europe regularly traded with Africans. And though the peasants were unlikely to, more wealthy individuals certainly did travel to Africa.)
The khara of Persia was a giant donkey with a single horn growing from its forehead. It had only three legs, but six eyes. It had protective powers of much the same sort as unicorns the world over, and it was important in the Zoroastrian religion.
The unicorn of European myth was smaller than a horse and had characteristics combining a horse, goat and deer. It always had dainty cloven hooves, not heavy horse-hooves. The idea that a unicorn looks exactly like a horse except for its horn is an invention of modern fantasy art.
Unicorn sightings from many areas of the world have caught the attention of explorers and scientists for hundreds of years. For a long time, people were generally expecting that unicorns were going to be discovered one of these days. Unicorns always seemed to be just around the corner, and there were many relatively unexplored corners of the world where they presumably might lurk.
Eventually, this expectation faded. Unicorns did not get discovered, and the number of sightings faded too. Yet, there are still some cryptozoologists today who think that so much hoopla could not have been based on nothing.
It's commonly believed that Unicorns were misidentified Rhinos, or perhaps other animals such as deer or elk with deformities.