Sana was asked by vishal to reherse with a violinist for a shot in the film, Wajah Tum Ho and when they were supposed to shoot it. Sana came to vishal and told him i am sorry but i didnt rehersed and the violinists told same to vishal, that she is not able to do it.
Vishal was left with no choice but to go ahead with shoot and see how it turns out. When they started the shoot, Sana played it so beautifully and the director was stunned with her. Then he realised that sana was playing a prank on him. The bit she played is retained in the film too