Merrie Melodies - A Wild Hare (1940)

A Wild Hare is a 1940 Warner Bros. Merrie Melodies cartoon supervised by Tex Avery. The short subject features Elmer Fudd and Bugs Bunny, the latter making what is considered his first official appearance.
Notes:
The film was nominated for an Academy Award for Best Short Subject: Cartoons but lost to "The Milky Way", another MGM Rudolph Ising production.
When the film was reissued as a Blue Ribbon release, it was retitled The Wild Hare. Also, during the "guess who" sequence, the name Cawole Wombard was redubbed, since Lombard died in a plane crash, and was replaced by Bawbawa Stanwyck.

What's up, Doc?
Bugs' nonchalant carrot-chewing stance, as explained many years later by Chuck Jones, and again by Friz Freleng and Bob Clampett, comes from the movie It Happened One Night, from a scene where Peter Warne (played by Clark Gable) is leaning against a fence eating carrots more quickly than he is swallowing (as Bugs would later often do), giving instructions with his mouth full to Ellie Andrews (played by Claudette Colbert), during the hitch-hiking sequence. This scene was so famous at the time that most people immediately got the connection.

The line "What's up, Doc?" was added by director Tex Avery for this short. 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. Because of the overwhelming reaction, Bugs eats a carrot and utters some version of the phrase in almost every one of his cartoons after that, sometimes entirely out of context as compared to this original use.

Caricatures:
Artie Auerbach - as his character Mr. Kitzel, "Mm, could be."
Mischa Auer - "Confidentially, you know..."