The Godfather – The Cat
The eternal classic 1972 mobster saga, The Godfather was a remarkable film for many reasons. While most of the masterpiece was planned, there was at one magnificent scene that was indeed unrehearsed.
The Godfather Wiki
Vito Corleone (Marlon Brando) has a scene where he explains about friendship to undertaker Bonasera (Salvatore Corsitto). The mafia boss is seen nonchalantly holding a cat. According to director Francis Ford Coppola, he actually found the stray cat on set and gave the actor the offer he couldn’t refuse.
The next ad-lib is from an Oscar-winning WWII drama.