On today's show , we talk about something found all over the world – the fly . When you spend time outdoors in nice weather , you usually come across a fly or two or … many ! Flies perform an important job in nature . They break down a lot of organic materials . Plus , farmers can use their larvae as very cheap food sources for animals . Those are really good things . But let's be honest : Flies are annoying ! They fly around our heads . They lay eggs in our trash and leave germs in our food . And they are so common that we often do not notice them . Once inside a building , they stick to the walls and seemingly watch the goings-on around them … secretly . And that brings us to today's expression – to be a fly on the wall . “A fly on the wall ” is a person who observes a situation without being noticed or without interfering . This expression has appeared in different forms in many old stories.Take for example , some lines from Shakespeare's Romeo and Juliet from the late 1590s . The language does not take the exact form of the expression “fly on the wall .” However , some experts suggest that the meaning of the expression is there . And so , the expression as we know it today began to take shape . Romeo wants to see Juliet's lovely hand and kiss her soft , red lips . But he can't . He is banished . The flies , however , are free . They can get as close as they want to Juliet . And Romeo sounds a bit upset about that . Now , let's hear that selection from an 1821 version of Romeo and Juliet : Today “fly on the wall ” remains a commonly used phrase . When you are a “fly on the wall ,” you are eavesdropping . You are listening in . You are a bystander , a witness and , sometimes , a spy . As an adjective , “fly-on-the-wall ” describes a style of filmmaking . Filmmakers and videographers often use the fly-on-the-wall method for reality shows and documentaries . The filmmakers tell the subjects to ignore the cameras and filming crew . Even if the camera is clearly visible , the film subjects usually get used to the cameras and forget they are there . Now , let's listen to this conversation between two roommates . I am SO happy it's Friday ! Hey , do you want to see a documentary that just came out ? It's playing at the movie theater near our apartment . What's it about ? It's a documentary about the lives of elephants ! So , you really feel like you're just hanging out with the elephants . I love elephants ! Now , we will use this expression in a natural conversation . For that , I have invited Kelly Jean Kelly into the studio with me . And that's all the time we have today . And I'm Kelly Jean Kelly .