It so happened that the duo was filming a romantic song in New Zealand's countryside and were supposed to run to each other, and fall into a long embrace. Sonam was then asked to lean on Imran's arms, reminding the audience of the signature Raj Kapoor-Nargis Dutt pose from the RK movies.
Director Punit Malhotra wasn't impressed with the first few takes, so he asked Imran and Sonam to lend more grace to the move, which tired out Imran.
However, it ended up being a total disaster as Sonam rushed into his arms and Imran leaned back with a little gush of enthusiasm, thus losing his grip. Both the actors lost their balance and came down with a thud.
To make matters worse, Sonam fell on some cow dung left back by a cattle grazing nearby. Poor Sonam had to immediately rush for a shower. The only saving grace was that the actress' costume, which got spoilt in the bargain, was not needed in any other shots.
Guess magic like Raj Kapoor's can't be created, it just happens on it's own!