We all know that in the land of the living, humans are mostly made up of water, but what happens when someone comes back from beyond the grave? How do they manifest into a ghost, and what are spirits physically made of?

The defining property of a ghost is its lack of flesh. It's not made up of organic matter, blood, and organs like a living human. But if people are able to sense the presence of a ghost, detect them with ghost hunting gadgets, or even see an apparition, then there must be something measurable and tangible that creates them.

To answer this question, we first need to break ghosts down into a couple of types of hauntings. There's a belief within the paranormal world that some ghosts are intelligent and capable of interacting with their surroundings, and then there are residual hauntings, which are said to merely be past events...