If you believe in ghosts, you're not alone. Cultures all around the world believe in spirits that survive death to live in another realm. In fact, ghosts are among the most widely believed of paranormal phenomenon: Millions of people are interested in ghosts. It's more than mere entertainment; A 2019 Ipsos poll found that 46% of Americans say they truly believe in ghosts. (The nation is discerning in its undead beliefs; only 7% of respondents said they believe in vampires).

And about 18% of people say they have either seen a ghost or been in one's presence, according to a 2015 Pew Research study. Why do so many claim to have such brushes with the afterlife?

"One common cause may be pareidolia, the tendency for our brains to find patterns (especially human faces and figures) amongst ambiguous stimuli," Stephen Hupp, clinical psychologist and professor at Southern Illinois University Edwardsville, Told Live Science in an email. "One common example is when we see faces or figures in the clouds and another is when random shapes and shadows in a dark house look like a ghost," said Hupp, who is also the editor of Skeptical Inquirer magazine.