Tex Avery (1940)
Bugs’s nonchalant stance, as explained many years later by Chuck Jones, and again by Friz Freleng and Bob Clampett, comes from the 1934 movie It Happened One Night, from a scene where Clark Gable’s character is leaning against a fence eating carrots more quickly than he is swallowing (as Bugs would later do), giving instructions with his mouth full to Claudette Colbert’s character. This scene was so famous at the time that most people immediately saw the connection.
The line, “What’s up, Doc?”, was added by director Tex Avery for this film. Avery explained later that it was a common expression in Texas where he was from, and he didn’t think much of the phrase. But when this short was screened in theaters, the scene of Bugs calmly chewing a carrot, followed by the nonchalant “What’s Up, Doc?”, went against any 1940s audience’s expectation of how a rabbit might react to a hunter and caused complete pandemonium in the audience, bringing down the house in every theater. As a result of this popularity, Bugs eats a carrot and utters some version of the phrase in almost every one of his cartoons; sometimes entirely out of context.