Factual error: Lord Rama is shown holding the bow in the right hand and raising the left hand for blessings. In Hindu practice the blessings are always given by right hand.
Factual error: No version of "Who Wants to be a Millionaire", regardless of what country it is in, allows for a bathroom break after the question has been posed and before that question is actually answered by the contestant. The show is pre-recorded with scripted times for breaks. Jamal could never have been in the bathroom where the host gives him a fake answer to a question posed but not yet answered. This clause is in the contract of all contestants who appear on the show.
Factual error: When Jamal is lowered from the roof of the train, Salim is seen from below leaning way over the edge of the train. Because of the curvature of the roof, and the fact that he was supporting Jamal but the rope wasn't anchored to anything, there's no way Salim could have leaned over that far.
Factual error: Mr. Vikas Swarup's book refers to "Ankhiya Hari Darshan Ki Pyasi" as the song by saint-poet Surdas. The song, Darshan Do Ghanshyam Nath Mori Ankhiya Pyasi, that features in the movie, is from 1957 film Narsi Bhagat which was directed by Devendra Goel. The film was based on the life of 15th Century Gujarati saint-poet Narsinh Mehta, who was a devotee of Lord Krishna. The song, based on one of the oldest ragas-Rag Kedar, was written by eminent Hindi poet and Bollywood song writer Gopal Singh Nepali and not Surdas as the movie claims.
Factual error: One of the questions Jamal has to answer is "Who invented the revolver?" to which the answer is given as Samuel Colt. Colt didn't invent the revolver, or even claim to invent it - he merely took a form which had existed for many years and substantially improved it. For example, Elisha H Collier patented a flintlock revolver in 1818 when Colt was only 4 years old which was produced in numbers for the British forces in India. More info: http://en.wikipedia.org/wiki/Elisha_Collier.
Answer: I believe it was to demonstrate that as a "slumdog" he knew some things but not others. He obviously did not know the answer to the question asked on the game show that the police chief asks him about, so to defend himself, he proves that he DOES know some things: just things that not everyone knows.
Brad