[moeris]

Just to add to other things people have mentioned, reports of ghosts could very easily be the result of false memories, as well. Finding a dead body in a creepy location, then sitting on it for two years is plenty of time and fuel for false memories. (Which are notoriously easy to form.)

Another thing I think is the most likely is [pareidolia](https://en.wikipedia.org/wiki/Pareidolia). Our minds evolved to be sensitive to seeing faces/hearing voices, and so we tend to see these things where they don't actually exist. (Think faces in toast, or listening for satanic messages when playing music backwards.)