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. There is not a drop of water inside the mine in reality now.
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.
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 slaughter house scenes were actually shot in a slaughter house in Prayagraj. The back story of Sultan Qureshi (played by 'Pankaj Tripathi') of a fearsome butcher who at the age of 12 could slaughter and skin 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.
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
Anurag Kashyap: [hidden camera] 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)
Anurag Kashyap: [long take] The first shot contains a long take lasting about 10 minutes, where a group of shooters walk through alley-ways to attack a house.