Willy Wonka & the Chocolate Factory
Director Mel Stuart knew that Gene Wilder would be the perfect Willy Wonka before Wilder even read for the part! Thus, Wilder had some leeway. Before accepting the role, Wilder insisted he would only take it if he could alter his character’s entrance. Seriously, it was Gene Wilder who came up with the wild entrance where Willy limps to the gate with a cane but then stumbles into a lively summersault! He thought this would set the audience up to mistrust his character throughout the film.

Willy Wonka & The Chocolate Factory
RoboCop
At times, directors feel it’s best to withhold some information from the rest of the cast so that they can capture the most genuine reactions. Thus was the case when Kurtwood Smith told director Paul Verhoeven about improvising a line. Both Smith and his director chose to surprise the cast during the scene where Clarence Boddicker (Kurtwood Smith) was taken by the police after RoboCop beat Boddicker. So when Kurtwood Smith shouts out, “Give me my f***in’ phone call,” the entire cast was actually in shock.

RoboCop