Amitabh Bachchan had the entire climax re-written, as he felt that it revolved around the younger leads and not on him. He asked the makers to re-write his role.
Madhavan was very excited to work with Amitabh Bachchan, and was thankful for Arshad Warsi declining the role, as it was Madhavan's long-cherished dream to be in a full fledged role with Bachchan.
In having many cameo appearance by key actors and actresses, Director Leena Yadav responded that there was relevance of the cameos and they all come into different situations and different games. Each of the actors and actresses has an impact on the plot, and hasn't been added on just to make the movie look bigger. The characters act as a ladder which lead the story to the climax.
Ever since Gandhi (1982), Sir Ben Kingsley wanted to feature in a Hindi movie. It took him twenty-seven years for this to happen with this movie.
Sir Ben Kingsley was added to the movie cast late on. Amitabh Bachchan's character is meant to be a genius at math who looks up to someone as the ultimate genius. Even though this character was in the script, the actor was not finalized. Keeping Mr. Bachchan's stature in mind, it had to be somebody that had a very strong screen presence, and it had to be a brilliant actor. The first actor that came to Director Leena Yadav's mind was Kingsley. The producer approached him, and he really liked the script, so he agreed to be a part of it.