A cold war prevailed between Mehmood and Manoj Kumar during the making. The latter even tried to influence the director so as to discard the song 'Hum Kaale Hain Toh Kya Hua' (picturised on Mehmood) from the film. However, the song was retained and it proved to be a smash hit and one of the highlights of the film.
Mehmood was the Highest paid actor in this movie .more than manoj Kumar and nanda which lead to a cold war between them..More from manoj Kumar
The film is an adaptation of the book named "And then there were none" by Agatha Christie.
Footage from the movie is used in the film Ghost World (2001). The main character, Enid, is dancing along to the big dance number "Jaan Pehechaan Ho" as the film begins.
The shooting of Gumnaam began in April 1964 and ended only in January 1965 due to the busy schedules of Nanda, Pran and Helen.