"'Eh, What's up Doc?' joins 'That's All Folks!' as the best-known lines from Tex Avery's Looney Tunes cartoon series. It was delivered by Bugs Bunny, while nonchalantly chewing on a carrot, in most of the cartoons in which the character appeared, beginning with A Wild Hare, 1940."
"Chuck Jones went on to explain that the demeanour of Bugs when delivering the line was adapted from Clark Gable's performance in It Happened One Night. In that film, Gable's character leans against a fence eating carrots and gives instructions with his mouth full to Claudette Colbert's character. The scene was well-known to audiences at the time who would have been well aware that Bugs was spoofing Clark Gable."