In the scene where Sue says 'Undher say awaaz aye gee' and the Sukhi burps, Karan throws his cigarette on the floor and steps on it quite audibly. Then in the very next shot he does it all over again and the 'undher say awaaz' scene is still going on.
Approximately 66 minutes into the film, Kirron Kher's character Mitro says that Udham Singh killed General Dyer, the brigadier-general responsible for the Jallianwala Bagh massacre, but in reality he killed Michael O'Dwyer, the former lieutenant governor of the Punjab in India.
During one of the flashback sequences set prior to 1947, the historical characters are on the roof of a building; in the distance is another building with a large satellite dish on its roof.
They never explain how they got an actor to play Mr McKinley.
In a scene of Aamir Khan wheeling his bike, it's too obvious that it's a stunt rider.