2. 1973 - The Movie Story: A pair of priests attempt to exorcise a demon that has possessed a 12-year-old girl living in the Georgetown neighborhood of Washington, DC.
The Real Story: William Peter Blatty was inspired by an article he read in college at Georgetown University about an exorcism performed on a 13-year-old boy in Mount Rainier, Maryland in 1949. The story's details have been muddled through the years -- perhaps intentionally so, in order to protect the family -- but the boy's actual home lay in Cottage City, Maryland, and the exorcism was performed in St. Louis. Evidence points to the boy's behavior not being nearly as outrageous or supernatural as was portrayed in the film.

4. 1975 - The Movie Story: A 25-foot-long great white shark terrorizes the fictional Northeastern fishing community of Amity Island, attacking swimmers and boaters for several days during the summer.
The Real Story: Screenwriter and novelist Peter Benchley was inspired in part by a series of shark attacks that plagued the New Jersey shore in 1916. Over a 12-day period in July of that year, five people were attacked, four of whom died. A seven-foot-long great white shark was killed on July 14, and its stomach was found to contain human remains. To this day, there is a debate over whether or not that shark was the culprit -- some scientists argue that it was probably a bull shark -- but no further attacks were reported that summer after it was killed.

6. 1977 - The Movie Story: A family driving through the southwestern desert in an RV takes a short cut that leads them to run headlong into a family of violent cannibals who live in caves in the hills.
The Real Story: The movie was inspired by the legend of Alexander "Sawney" Bean, a Scottsman of the 15th or 16th century who reportedly headed a 40-person clan that killed and ate over 1,000 people, living in caves for 25 years before being caught and put to death. His life has inspired numerous stories and films worldwide, including British film Raw Meat, but most serious historians today don't believe that Bean ever existed.

8. 1982 - The Movie Story: Carla Moran, a single mother of three, is plagued by a supernatural entity that abuses and rapes her repeatedly. She receives help from paranormal researchers, who document the haunting and attempt to trap the spirit.
The Real Story: In 1974, paranormal researchers Kerry Gaynor and Barry Taff investigated the case of a woman believed to be named Doris Bither. Bither lived in Culver City, California and claimed to have been physically and sexually assaulted by an entity. Gaynor and Taff witnessed objects move in her house, captured photos of floating lights and saw a humanoid apparition, but they never saw it assault the woman and never tried to capture it. Gaynor stated that the attacks diminished when Moran moved.

10. The Movie Story: In 1816, poet Lord Byron gathers fellow poet Percy Shelley and his soon-to-be-wife Mary, along with Mary's half sister Claire and Byron's doctor, John Polidori, at his Swiss mansion. They tell ghost stories and experience surreal supernatural encounters that are physical manifestations of their fears.
The Real Story: In the rainy summer of 1816, Percy Shelley and Mary Godwin (soon to be Shelley) visited Lord Byron at his Swiss villa. Due to the rain, they stayed indoors discussing the animation of dead matter and reading German ghost stories. Byron suggested they each write their own supernatural tale, and Godwin came up with Frankenstein, while Byron wrote what would later be adapted by Polidori into The Vampyre.

12. 1988 - The Movie Story: American anthropologist Dennis Alan is hired by a pharmaceutical company to acquire a sample of a drug used in Haitian voodoo rituals, a paralyzing powder that simulates death.
The Real Story: The movie is an exaggerated adaptation of a 1985 book by Canadian scientist Wade Davis, a nonfiction account of his experiences with zombification in Haiti. He stated that a powder of natural toxins could be used to place a victim into a death-like state, to be resuscitated in a hypnotic trance by a controlling "master." One notable case referenced was that of Clairvius Narcisse, who reportedly served as a zombie for two years in the 1960s. There remains a debate over the veracity of Davis's claims.

14. 2003 - The Movie Story: When unmarried couple Daniel and Susan take a group scuba diving trip, a mistake by the crew while taking a head count of the divers who return to the boat leaves the couple floating alone in the ocean, surrounded by sharks.
The Real Story: In January 1998, married couple Tom and Eileen Lonergan disappeared off Australia?s Great Barrier Reef after a diving company accidentally left them behind in the water. It took two days -- when a bag containing a wallet and passports was found -- for the crew to realize that they'd left the couple behind. A search was conducted, but their bodies were never found. Belongings discovered weeks later showed no signs of the violent shark attack that the film suggests.

16. 2005 - The Movie Story: Two female British tourists and an Australian man venture into the Australian Outback to camp in Wolf Creek National Park. When their car breaks down, they're rescued by a tow truck driver who ends up holding them captive and torturing them.
The Real Story: Greg McLean originally wrote the script as fiction, but upon learning of two real-life Australian killers who attacked travellers, he edited the story to reflect the real cases -- namely, Bradley John Murdoch, who killed a British tourist and tried to abduct another in July 2001, and Ivan Milat, who picked up hitchhikers and took them into the woods to torture and kill them during the '90s. Both Murdoch and Milat were captured and sentenced to life in prison.

18. 2007 - The Movie Story: An American news crew travels to Burundi to chronicle the capture of a man-eating crocodile, which ends up being 30 feet long and responsible for over 300 deaths.
The Real Story: The story is based on Gustave, a 20-foot-long crocodile living in Burundi that is believed to be the largest crocodile on record on the African continent. It is rumored to have killed 300 people, although that number is almost certainly inflated. High-profile attempts to capture Gustave have failed, and the creature, believed to be over 65 years old, still lives in the Ruzizi River area of Burundi.

20. 2009 - The Movie Story: The Campbell family moves to Connecticut to be near the doctor caring for their ill son, Matt. They soon realize that their new home is a former mortuary haunted by a malevolent force.
The Real Story: The film's inspiration was the Parker family, who moved to Connecticut in 1986 to be close to the specialists treating their 14-year-old son, Paul, for cancer. In the basement, where Paul slept, they discovered embalming equipment that implied that the house had been a funeral home. They reported encountering unexplained phenomena, like bloody floors, disembodied voices and shadowy figures. Paul became possessed by a force that caused him to attack his family. Eventually, an exorcism was performed to cleanse the house.