For all his musical genius, R. D. Burman surely wins hands-down for some of the most incomprehensible singing in Hindi film music. This makes it possible to build up nuggets of trivia or just moments of revelation when everything suddenly becomes clear (long live headphones for that).
Trivia nugget: Listen to his opening screech on his famous duet with Asha in APNA DESH (remember the unintentionally hilarious dance sequence with Rajesh "I hate tears" Khanna and Mumtaz with garish lights and psychedelic costumes -- sheesh!) "duniya mein logon ko". Guess what? his scream is actually an effective verbal distortion (something he should have patented while he was still alive) of the simple English word 'sweetheart'.
General moment of revelation: his cross-line for the 'tum kya jaano segment' of the medley in HUM KISISE KUM NAHIN. Here are the words for the chicken-hearted who dare not venture on this voyage of discovery (titter, titter!): 'suno kehna hamara/ameeri hai sitara/gareebi ek aansoo/yeh aansoo hai mohabbat/mohabbat zindagi hai' and the rest being the easily audible 'bas itna jaan le tu'...