"The Exorcist" was a major game-changer for the horror genre when it was released back in 1973, and the shockingly strong performance from 14-year-old Linda Blair was a big reason for the film's runaway success. Blair played Regan MacNeil, a young girl possessed by a violent, foul-mouthed, Latin-speaking, head-spinning demon, and her performance was so convincing that she reportedly received death threats and hate mail from people who thought she was "glorifying Satan." But that's far from the only thing that haunted the young actress once filming on "The Exorcist" wrapped. This is how "The Exorcist" transformed Linda Blair forever.