Early modern naturalists used the term "Lusus Naturae" (meaning 'Jokes of Nature') to describe any creature or object that defied classification. The concept represented the belief that Nature enjoyed playing jokes on man by confounding his expectations — in other words, that Nature played hoaxes on man. One famous example of a Lusus Naturae was the "Vegetable Lamb." Believed to be a real creature, this was a lamb from whose belly grew a thick stem firmly rooted in the ground. Thus, it was part plant, part animal, but didn't belong wholly in either category.
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The History of Hoaxes