I remember one time I heard this English professor asking the class what the world's scariest noise is. Is it a man crying out in pain? A woman's scream of terror? A gunshot? A baby crying? And the professor shakes his head and says, 'No, the scariest noise is, you're all alone in your dark house, you know you're all alone, you know that there is no chance anyone else is home or within miles—and then, suddenly, from upstairs, you hear the toilet flush.