A changeling, also historically referred to as an auf or oaf, is a human-like creature found throughout much of European folklore. A changeling was a substitute left by a supernatural being when kidnapping a human being. Sometimes the changeling was a 'stock' (a piece of wood made magically to resemble the kidnapped human), more often the changeling was a supernatural being made magically to look like the kidnapped human.
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Supernatural beings blamed for stealing children included fairies, demons, trolls, nereids and many others. Usually, the kidnapped human was a child; but there were cases, particularly in Scandinavia and Ireland, where adults were taken.