For Server Sundaram
Nagesh actually worked in a Canteen as a waiter for 5 weeks on Saturdays and Sundays where he learnt to stack tea tumblers and arrange plates. The owner knew who he was as did the staff but he changed his appearance and called himself VISWA and many customers remarked how he looked just like Nagesh 😁
For Jo Jeeta Wohi Sikandar
Though the end scenes were shot with dupes, Aamir Khan personally learnt how to ride GEAR BIKES and even fell down 4–5 times
For Ethiroli
Sivaji went to multiple hearings in High court to observe barristers behaving
However he created so much diversion due to his popularity that the Judges asked him not to come anymore
He engaged Retd Justice Srinivasan to coach him later
For Visaranai
Dinesh and Murugadoss were asked by Vetrimaaran to spend a few days in Judicial Custody under false names to find out how the system worked
They got permission from the District Collector of Nellore to pretend to be accused and spend 4–5 days in JC
Samuthirakani was shown how beatings were administered and HE WAS SHAKEN when he saw the entire thing
For Maharaja
He actually learnt how to use the Barbers Razor to shave and even how to cut hair
Anurag Kashyap even asked VJS to actually shave him for the scene but the insurance advisor said NO
For Pannaiyarum Padminiyum
VJS learnt to drive a tractor and quite well
For Aadukalam
Vetrimaaran lived for 2 years in Madurai under the name Sivagnanam and ate at local restaurants every day to pick up the accents, dialects and mannerisms
Dhanush , Kishore , VM and Ambrose (Jacki Ambrose the art director) visited multiple cock fights to observe how local cockfighters worked
They even got caught in a raid
Dhanush actually took 4 Cockerels home for a few weeks to months to get acclimatized to them
For Parthen Rasithen
Raghuvaran LEARNT how to make Dosas and literally became an expert on Dosas
Actor Charles Dance who played Tywin Lannister ACTUALLY LEARNT HOW TO SKIN A DEER and perfected his role than use a decoy or camera transition