Rajinikanth said his contemporary Kamal Hasan possibly knew what that something was, but might not want not share the secret with him.
The two stars were among a host of dignitaries at the inauguration of a memorial constructed by the Tamil Nadu government for the iconic actor Sivaji Ganesan.
To press his case, Rajinikanth cited the instance of the late thespian, saying that he could not succeed in politics despite being immensely popular.
"Sivaji (Ganesan) has left a lesson not just in cinema but also in politics. He started his own political party, fought and lost (elections) from his own constituency. This was not an insult to him, but the people of that constituency," he said at the function, attended by Deputy Chief Minister O Panneerselvam and Haasan, among others.
"But even if he knows it, he won't share it with me," he said, as the gathering laughed.
Tamil Nadu has had a rich history of cinema marrying politics. Mr Ganesan's contemporary, M G Ramachandran, not only floated the AIADMK after walking out of the M Karunanidhi-led DMK, but also went on to become the state chief minister.
Of late, both Haasan and Rajinikanth have been indicating that they may join politics, with Mr Hasan taking repeated potshots at the ruling AIADMK over issues such as corruption and the spread of dengue.