It can be very bothersome when a song gets stuck in your head and you cannot resist yourself from humming it all the time. Things get more disturbing when you lose your concentration and focus. Sometimes we cannot even recall when we heard the song or where but still the same lines repeat themselves in our mind. Funnily this happens more when we need to concentrate on some hard task. Such a bugging song is aptly referred to as an earworm. There are many theories regarding this strange phenomenon that may persist for days.
One of the reasons why a song gets stuck in your mind is that you are not interested or engrossed in the work you have undertaken. Light and boring jobs can get your mind hum something that it took fancy to. The earworm theory says that a particular song or stanza gets stuck to our mind due to the brain-itch. This means the song scratches the brain itch and increases the demand for further scratching. The auditory cortex of our brain keeps a record of the songs we listen to and can repeat the music or words we liked.
Even a difficult and trying job can make our brain hum the same lines of a song several times. Listening to the same song lots of time can also have the same effect on our head. Sometimes we hear a tune which either attract us or seem odd and our brain starts repeating it without stop until we get the heck of it. When truly like a song we keep on listening to it and humming it hundreds of times. Some songs we hum without stop because they reflect our inner state of mind. When we are tensed, stressed or very happy we choose songs that reflect our psychology.