 Supernatural horror was further increased by the pulsing heart-beat which heralded its every entrance.This sound, Olivier remembered, had been used by Jean-Louis Barrault in a stage production in Paris; he made it doubly effective on the screen by bringing the camera in and out of focus to synchronize with the pulsing.Before he would use it, however, he wrote to ask Barrault's permission and insisted on paying for the idea.