This is the song, "Kal Kya Hoga Kisko Pata", that starts with the corny, 'Prani Bhatak Raha Hain' prelude sung on screen by Bhagwan Dada. The scene during the song is to showcase the carefree life of Randhir Kapoor's character, and the song's lyrics go in-sync with that attitude.
For comparison, the film's Tamil version, Dharmathin Thalaivan, starring Rajinikanth in Amitabh's dual roles, Suhasini and Prabhu, had a similar set-up where Prabhu goes out with his friends and has the "Yaaru Yaaru Indha Kizhavan" song. The difference is that Rajinikanth's professor character participates in the song in a disguise (the 'Kizhavan', or old man, referred to in the song), playing Bhagwan Dada's role!!
Coming back to "Kal Kya Hoga…", the song starts with a unique Pancham-style free-form 'Arrrr rapa' singing (that also features in the middle of the song) before moving to the actual 'Kal Kya Hoga' part.
In the film, with the extended prelude:
The song's tune for the entire mukhda, including the opening 'Arrrr rapa' phrases are inspired generously by a 1975 African/Swahili song called "Hafanana", by the singer Afric Simone.
Afric Simone speaks German, English, Portuguese, French, Spanish, and various African languages, but his songs are written in the mixture of Swahili and few words from other languages.
The original starts with
"Trrrrr chacha, trrrrr ha ha
trrrrr voom bam, trrrrr ha ha",
that corresponds directly with Pancham's opening.
But, this is not the last inspiration of Afric Simone's song in Hindi cinema.
Almost 2 decades after Kasme Vaade, Anu Malik found the tune useful to open his song, "Rabbi Re Ralli", in the Bollywood freemake of Sleeping with the Enemy (1991): Yaarana (1995).
As if not satisfied with using the tune once, another decade later, in 2005, Anu Malik used it again, for the song, "Hot Hot (Kalyug Ki Laila)"!