Well, If you’re Virender Sehwag, then the only thing going on in your mind while batting is a tune of a hit song, or a “bhajan”. Cricketers like him, often like to take the pressure off themselves while batting by singing to themselves or humming a tune.
It might also be used by a batsman to taunt a bowler by showing him that he could even hit him for a six while not concentrating completely, or who knows? – it could also be used to scare off or irritate a bowler with his “bathroom singer” voice.
This brilliant strategy is also used by the batsman to entertain themselves so that they do not get bored of defending the ball for a long time. Hmmm...I wonder if Rahul Dravid ever used this tactic while defending the ball over and over and over and over again.