 The first 30 minutes of the film has a background noise with a  frequency of 28Hz (low frequency, almost inaudible), similar to the  noise produced by an earthquake. In humans, it causes nausea,  sickness and vertigo. It was the main cause of people walking out of  the theaters during the first part of the film in places like Cannes  and San Sebastian. In fact, it was added with the purpose of getting  this reaction.