Commonly mistaken as an ‘imaginary friend’, the cavum amicus can possess objects and living creatures. Luckily, they are usually harmless and generally friendly creatures. They are only visible and audible to their current host, and thus often mistaken as an ‘imaginary friend’, and in some cases even multiple personality disorder, schizophrenia, or haunting.

This creature is also capable of possessing inanimate objects, but the object must be somehow emotionally connected to the host. Traditionally, people would craft dolls ranging from woven twigs to clockwork automaton to house these "spirits". They would often weave in an item of emotional significance into the doll, allowing the creature to possess it. This allows the creature to have a body of its own, to interact with the physical world.

It is speculated in folklore that they are spirits created from strong emotional stress, and they were treated with great respect as they felt that the "spirit's" purpose was to help their host overcome these hardships. Unfortunately, there is no specific evidence as to exactly where they come from or how many there are due to their ethereal nature.

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