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What do scientists say about ghosts?
ARE ghosts real? It's the million dollar question that has never truly been solved but here are some theories from experts which debunk them.
Two scientists have provided rational explanations for why people see ghosts, which - while abnormal - are not paranormal.
Their findings form part of a BBC Three investigation, which has become the latest attempt to try to find a scientific explanation for ghosts and ghouls.
Sleep Paralysis
Many ghost stories can be explained by sleep paralysis, according to Dr Chris French, who heads the Anomalistic Psychology Research Unit at London's Goldsmiths University.
As people fall into rapid eye movement (REM) sleep, their bodies remain frozen in sleep mode while their brain is active.
This is when people can find themselves awake but unable to move.
According to the NHS website, it feels like someone is in your room, or like something is pushing you down.
Hallucinations can also arise in a "small percentage" of sleep paralysis cases, French explained.
“Sleep paralysis is a kind of glitch in the normal sleep mechanisms,” he explains.
“It can be terrifying. One student of mine told me about waking up and there’s a black cat by the side of the bed hissing at him.
"But it had an inverted cat skull with black goo dripping from its mouth.”
Prior Belief, Context & Hallucinations
There's a three psychological reasons why people might believe in ghosts: prior belief, context and hallucinations.
If someone tells you a place is haunted, you'll notice every chill, creak and shadow.
It makes psychological sense.
It's like when you learn a new word, and suddenly see it everywhere.
“When people hear the word ghost... you visualise ghosts walking through walls rattling chains," French continued.
"People do report stuff like that, but it's very rare.
“It's much more likely to be more vague sensations.
"A sense of presence. Feeling dizzy, changes in temperature, shivers up the spine."
Context is also key, French explained.
“If you’re shown around an old building and somebody says it’s haunted... you'll notice every little creak and change in temperature in a way you wouldn't have done otherwise.”
Electromagnetic Fields
Electromagnetic fields are invisible areas of radiation that travels in waves.
They can comes from both natural and man-made sources.
But in rare instances, they can cause disturbances in people’s brain signals, prompting hallucinations.