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Do you believe in ghosts? If so, have you ever seen one? If you answered "yes" to both questions, you are not alone. In fact, a number of surveys found that the majority of people who took part believe in ghosts, with a high percentage claiming that they have seen them.

The belief in the supernatural is an old one. For millennia, humankind have used it as a source of meaning, and continue to do so to this day. But while many people claim to have had paranormal experiences, science also has a word to say about this.

Click through the gallery to find out why people see ghosts, according to science.

▲A study found that about three in four Americans have at least one paranormal belief.

▲A survey commissioned by Grupon in October 2018 found that over 60% of the people surveyed have seen a ghost.

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Some people believe they see ghosts because they’re expecting to see ghosts. If they’re told that they’re in a haunted house, they’re much more susceptible to a paranormal experience.

▲A study conducted in 1997 put 22 people in a creepy theater. Half of the people were told that the place was haunted, and the other half was told the place was under construction. Can you guess which half saw or sensed something paranormal?

▲Half of these people were led to believe that something otherworldly might happen, so the group that was told they were in a haunted theater experienced it.

▲It's possible that some of the people who see ghosts have a brain malfunction. While investigating a woman’s epileptic seizures, a neurologist found that applying current to a certain part of her brain made her feel like there was a presence behind her, mimicking her.

▲Originally called the "Koren Helmet," it's a device that sends magnetic signals to one's brain. Built to study religious and mystical experiences, it can apparently trigger paranormal experiences.

▲Supposedly, some people claimed to have had visions of God during the experiment, while others felt a presence, among other paranormal experiences.

▲A study concluded that stress can cause women to report paranormal experiences. Traumatic stress was linked to experiences such as possession and extra-sensory perception.

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Maybe ghosts are just really low sound frequencies. More specifically, infrasounds, which are sounds below the normal range humans can hear.

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These frequencies can actually trigger physical and emotional responses akin to paranormal experiences.

▲What is a haunted spooky place without a bit of mold, right? Well, the truth is that certain types of mold can actually make you hallucinate, and affect balance and coordination.

▲People who've lost loved ones have reported being visited by them. The ghostly visits could be a coping mechanism used by the grieving brain.

▲Cold spots in a house, for instance, are believed to be a sign of paranormal activity. But a sudden change in temperature in a specific spot doesn’t necessarily mean you’ve encountered a ghost.

▲Changes in humidity levels, a drafty window, or a chimney might be responsible for the cold sensation at a specific spot.

▲A study found that ghostly activity was more consistently reported in known "haunted" locations. But environmental factors such as magnetic fields and lighting levels could be to blame.

▲In the 1920s, the Journal of Ophthalmology documented a case study about a couple who reported paranormal experiences at home.

▲It turns out that they were in fact having hallucinations, triggered by a CO leak in the furnace.

▲Exploding head syndrome happens when you experience a loud noise, usually when falling asleep or waking up. It’s like a phantom loud explosion.

▲This likely happens because the part of your brain responsible for shutting down your body to put you into a sleep state gets a bit confused, and does the opposite instead, putting you in a state of alert.

▲So that loud explosion you heard was not a ghost trying to blow up your house, but actually your brain being a bit out of sync.

▲Paranormal experiences are common during sleep paralysis. This phenomenon occurs when you’re in a dream state, but you're half-awake and unable to move. This is usually a confusing and sometimes terrifying experience.

▲Paranormal experiences are sometimes reported during this state of semi-consciousness. But the truth is, you’re likely dreaming.

▲Those little balls of light that so many people claim to be spirits, can actually be explained by science.

▲If not photographic evidence of spirits, what are these orbs then? Well, they can be a number of things, including dust, pollen, insects, moisture, or even just a dirty camera lens.

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Believing in ghosts does help us cope with our own mortality, and like any other belief system, helps us make sense of our place in the world.

▲That these celebrities also had paranormal experiences?