What is the best possible explanation for the first ghost seen

Early Ghost Sightings

In the first century A. D., the great Roman author and statesman Pliny the Younger recorded one of the first notable ghost stories in his letters, which became famous for their vivid account of life during the heyday of the Roman Empire. Pliny reported that the specter of an old man with a long beard, rattling chains, was haunting his house in Athens. The Greek writer Lucian and Pliny's fellow Roman Plautus also wrote memorable ghost stories.

Centuries later, in 856 A. D., the first poltergeist-a ghost that causes physical disturbances such as loud noises or objects falling or being thrown around-was reported at a farmhouse in Germany. The poltergeist tormented the family living there by throwing stones and starting fires, among other things.