Zmiennica

A zmiennica (Polish, plural zmiennice) is a creature from Polish folklore, most commonly described as a changeling. It is believed to be a child secretly swapped by demons or other malevolent beings, such as witches or evil spirits, for a human infant. The zmiennica typically appears to be a normal baby at first, but it is often characterized by unusual physical traits or behavior. These might include an insatiable appetite (especially for a grown person's portions), excessive crying, disproportionately large head or limbs, inability to learn to speak or walk at the expected age, or a generally sickly and weak constitution.

The motivation behind the swap varies in different tellings, but common reasons include a desire to replace a demon child with a human one, a need for a human infant to be sacrificed, or simple malice. The swapped human child is believed to either be held captive by the demonic beings or killed.

Belief in zmiennice served as a way to explain infant mortality, developmental delays, and other unexplained conditions. Mothers suspected of having a zmiennica might subject the child to cruel tests or treatments to force the demonic being to reveal itself and hopefully reclaim their original child. These could include leaving the infant exposed to the elements, throwing the child onto a dung heap, or pricking it with needles. Such practices, while reflecting the desperation and fear of the parents, are now recognized as harmful and rooted in superstition.

The concept of the zmiennica is similar to the changeling myths found in other European folklore traditions, particularly in Celtic regions.