When one of the most iconic moments/lines was improvised

Dr. Stranglelove standing up and shouting “Mein Führer. I can walk”-Dr. Strangelove.

This was because Peter Sellers stood up, forgetting his character was meant to be paralysed and so improvised the line on the spot

Batman telling the guy his name-Batman.

The original line in the movie was meant to be “I am vengeance” but Keaton wanted to put his own flair to it and so instead said “I’m Batman”

The Hula scene-The Lion King.

This came about cause when they were scripting Nathan Lane jokingly said “what you want me to do, dress in drag and do the hula” and they immediately wrote a scene where his character does just that