They needed a ugly dwarf of a woman for the film. Manoj use to see a lady begging around the Taj. She use to scare him. Manoj Kumar suggested her to Raj Khosla. Khosla sought out for her and signed the her . She created a real horror in the film. Manoj Kumar also pointed out there was one mystery in the film that was unsolved. The window wipers going off on their own when Sadhana stepped into Manoj's car. Raj Khosla said its ok , and leave the scene where it was. It would get people talking about it.
"Lagja Gale Se" song was initially rejected by the director when he first heard it . It was recorded only after he was convinced by Madan Mohan that it would be appreciated. Such was the popularity that Lata Mangeshkar's song has been covered by many other artists many years later.
"Naina Barse" was composed by Madan Mohan in 1952, but no filmmakers had a situation for the song. Over ten years later, Raj Khosla and Sadhna were looking for haunting music for Woh Kaun Thi, heard the song, and decided to put it in the film.
After a delay due to inclement weather, the film unit flew to Kashmir to film the song "Naina Barse", but singer Lata Mangeshkar was abroad performing a concert. Composer Madan Mohan provided the vocals while actress Sadhna lip-synced. Many local people went to see the shooting and were surprised to hear a male voice singing for the heroine. After the shooting was completed, Lata returned and dubbed the song.
Second of four mystery-thriller collaborations between actress Sadhna and director Raj Khosla; the others being: Ek Musafir Ek Hasina (1962), Mera Saaya (1966), and Anita (1967).