Question

what astonishing discovery did patol babu make in telling oh oh oh

Answer 1

Patol Babu discovered that no part is big or small for an actor. A true actor seize every opportunity and give his best performance even when it is a single word act. And one who do so is a true actor. 

Answer 2

When Patol Babu started rehearsing "Oh, oh, oh, oh, oh" for his scene, he realized the same exclamation, when spoken in different ways, carried different shades of meaning. A man when hurt said 'Oh' in quite a different way. Despair brought forth another kind of 'Oh'; sorrow provoked yet another kind. In fact, there were so many kinds of "Oh's"--the short "Oh", the long-drawn "Oh", "Oh" shouted and "Oh" whispered, the high-pitched "Oh" and the low-pitched "Oh", and the "Oh" starting low and ending high, and the "Oh" starting high and ending low. Strange! Patol Babu suddenly felt that he could write a whole thesis on that one monosyllabic exclamation.