" Chris explained. Beginning on the day after Regan’s birthday—and following Howard’s failure to call—she had noticed a sudden and dramatic change in her daughter’s behavior and disposition. Insomnia. Quarrelsome. Fits of temper. Kicked things. Threw things. Screamed. Wouldn’t eat. In addition, her energy seemed abnormal. She was constantly moving, touching, turning "

― William Peter Blatty , The Exorcist