Why do we Hum a tune?

For past few years I have been thinking about this or rather asking this question to myself but never thought of posting or asking in this blog. Why do we suddenly hum or whistle a song or a tune? How is it that a song suddenly comes to our mind out of nowhere? If we had listened to a song in a TV channel or in a FM in the morning, we are bound to hum the same song all the day or we usually hum a song we heard just few minutes of few hours back but what it means if you start humming a song which you don’t even remember the time you last listened to it?

Some of the songs that often comes to my mind are ‘Unnai Naan Arivaen Ennai Andri yaar Arivaar’ from Guna, ‘Vaan nilaa tharum oli ival vizhi’ from Kadhal Virus, ‘Bhaagere Mann’ from Chameli, ‘Unnodu vazhatha vazhvu’ from Amarkalam, ‘Kaatril varum geethamae’ from Oru Naal Oru Kanavu, first interlude of ‘Kanmani Anbodu kaathalan’ from Guna, version of ‘Paavana guru’ from Mella Thiranthadhu kadhavu and few others. Some of the songs that I have listed are classics and some may never come to my mind when someone suddenly asks us about my all time favourite songs.

I initially thought that it all depends upon the mood. Partially it is true; ‘Bhagerae mann’ always comes to me when it drizzles in Bangalore. But does it mean that it is the best rain song ever made. Why ‘Oh ho megam vandhado’ didn’t come to me. It definitely is a song that has more chances to come to any Tamilians mind while it is raining. Why it didn’t come it me? What does it mean? I seriously have to go back and analyze all different situations when each of the above songs came to me. I think I will definitely find an answer. If someone has already thought about this, please let me know why it is so. The more you try to understand the music, more mysterious it becomes.