Sardar Khan's son Perpendicular and his friend Tangent are seen watching "Munnabhai MBBS", a popular Bollywood movie released in 2003 starring actor Sanjay Dutt. Nawazuddin Siddiqui, who plays Faizal Khan Perpendicular's elder brother, played a blink-and-you-miss-him role in the same film when he was an unknown actor.
Most of the slaughter house scenes were single shot takes. After every shot, the actor 'Vipin Sharma' (who acted in the role of Ehsaan Qureshi) would come aside and throw up. The AD 'Anubhuti Kashyap' (sister of director Anurag Kashyap) would hold back a crowd of almost 50 by standers, more than half of whom were actual butchers, during the shoot by holding her arms wide. A lot of these butchers actually had knives and choppers hidden in their clothes and would joke among themselves "shall we plunge it stab it this way?" which she could hear, and had to ignore since she had to concentrate in the shoot
The music composer Sneha Khanwalkar started work on the soundtrack over a year before filming began. She traveled to places such as Trinidad in the West Indies to record Chutney music, a fusion of Caribbean and songs of Bihari migrants that were taken there in 1830s as slaves. "Hunter" is one such song, there were two more "Dumper loading unloading" and "British" that did not make it to the film.
The scene featuring a flooded coal mine (just before Sardar Khan is born) is shot in a real coal mine that was actually dry. Using the sound of water dripping and people wading through water, and actors walking as if struggling to cross water, they created the illusion of flooded mine in the darkly lit shot. For the safety of crew, there is not a drop of water inside the mine.
The slaughter house scenes were actually shot in a slaughter house in Allahabad. The back story of Sultan Qureshi (played by 'Pankaj Tripathi') of a fearsome butcher who at the age of 12 could slaughters and skins 1 buffalo in a single day was developed on actually seeing a boy do it. Similarly, Sultan in the contemporary time scale of the film could cut 60 buffaloes in a day. This too was developed seeing an actual person.
Assistant director Sohil Shah died in a freak accident during the shoot of the film in Banaras. He fell with a jeep off a bridge. Sohil hit his ear against a metal rod and suffered an instant hemorrhage.
In an unusual move for India, the movie was released in two parts, separated by a few months. The script was written to appear as two standalone stories when seen separately, but appear as a single story when seen together. The trailer for part 2 is shown after credits finish rolling in part 1.
Multiple chase sequences on crowded streets, among ordinary people and not hired extras. Anurag Kashyap uses hidden cameras to capture raw ambiance of the location in many of his movies, such as the slum chase in Black Friday (2004)
The trivia item below may give away important plot points.
The movie continues the trend of Anurag Kashyap paying tribute to Quentin Tarantino's directorial style. One particular example is of a person getting shot while the shooter is not in the frame, often unexpectedly. Shahid Khan, the main protagonist of the first third of the movie, gets shot unexpectedly while on Ramadhir's duty. Two generations later, his grandson, Faizal Khan and the protagonist of the last third, gets shot in the same fashion. Sardar Khan, Faizal's father, is the only protagonist not to be killed in this way. Instead in his case, the audience sees all four shooters but never see him actually getting shot. Anurag Kashyap had earlier made use of this effect in his movie Gulaal.