The Big B, says director Sujoy Ghosh, must be a part of each one of his movies in some capacity or the other. In Ghosh's Kahaani he has sung  Ekla chalo, the Rabindra Sangeet filmed on one of Big B's favourite actresses Vidya Balan.

Says Sujoy Ghosh, "I basically took to filmmaking for 5 reasons: Satyajit Ray, R.D. Burman, Anand Bakshi, Kishore Kumar and Amitabh Bachchan. After working with him in Aladdin I decided Mr. Bachchan would be part of every film that I make. I've two scripts Borivli Fast and Kabuliwala ready for Mr. Bachchan. I had no role for him in Kahaani. That is Balan's film all the way. So I persuaded him to sing in Bengali, a language he is quite familiar with—having spent a large part of his youth in Kolkata, being married to a Bengali and being considered Bengal's son-in-law. And Bachchan Saab sank Ekle chalo like a dream. He sang it better than any Bengali singer I've heard."

Now the trio of Big B, Vidya and Ghosh intend to take the Rabindra Sangeet forward, "It would be a pity to leave it at just one song. We have to carry Mr. Bachchan's amazing skill at singing Rabindra Sangeet further. You've no idea how much his singing has added to the film." Apparently the Big B's Ekle chalo helped Vidya emote in her most crucial scenes in Kahaani.

Recounts Ghosh, "Ekle chalo is about a human's solitary journey through life. And that's what Vidya's character in Kahaani does. Vidya seemed to grasp the nuances of Big B's rendition and put them in her character. There's  a scene at the beginning at the police station where Vidya just slumped in a chair in front of the cop. I asked her why.She said, 'The pregnant woman has travelled from the US for 14 hours, taken a taxi at the Kolkata airport and driven straight to the police station to inquire about her missing husband. Her walk and her sitting posture must define her immense fatigue. I think Mr. Bachchan's song helped Vidya find the centre of her character's solitary journey." About  further exploring the Big B aptitude for Rabindra Sangeet Sujoy says, "It's the logical progression from what he has done in Kahaani. Only the deaf would ignore what his rendition of Ekle chalo tells us."