Acclaimed Flop: Despite receiving a gala premiere at the Warner Bros. Theatre, following such a devoted production that the animators cheated their punch cards to buy more time to work on the short, it subsequently wasn't treated as anything special. It was at least submitted for an Academy Award nomination, but ultimately rejected. It took about two decades for What's Opera, Doc? to receive the respect it deserved, and even longer for it to receive acclaims of any kind (though boy, such acclaims - the first cartoon to get added to the Library of Congress's National Film Registry in 1992 and voted #1 of The 50 Greatest Cartoons in 1995.)
Consolation Prize: Some believe the Academy Awards giving the short's director, Chuck Jones, a Lifetime Achievement Award in 1996 was partially to make up for not giving What's Opera, Doc? an Oscar at the time of its release (as well as other notable Jones shorts like Duck Amuck or One Froggy Evening, neither of which even received a nomination).
Bugs Bunny is found dead while laid out on a rock, with some kind of fluid dripping on his face. This is a reference to Loki the Norse trickster god who was punished for causing the god Balder's death. Loki was laid out on a rock with snake venom dripping on his face as punishment. (Loki appears as a character in the first Ring Cycle opera "Das Rheingold," albeit under the German name "Loge.")
The ending is an inversion of the actual tragic ending of Siegfried and Brünnhilde's romance. In mythology and the opera ''Götterdämmerung," Brünnhilde has Siegfried murdered after he betrays her, only to be stricken with grief and remorse after he dies (and Driven to Suicide). Here "Siegfried" is the betrayed lover who kills "Brünnhilde," only to instantly mourn.
The Other Darrin: Though Arthur Q. Bryan otherwise voiced Elmer in this short, Mel Blanc performed "SMOOOOOOOOOOOOGGGGGGGGGG!" Word of God stated it was because it made it funnier and Bryan couldn't scream as loud as Blanc.
Bryan's read of the line can still be heard in the version used for the Bugs Bunny at the Symphony live performances.
Vindicated by Cable: According to a featurette on the Looney Tunes Golden Collection, Vol. 2, "What's Opera, Doc?" initially wasn't really any more recognized or popular than any of the other Looney Tunes shorts coming out during that time period. It wasn't until years later via TV reairings that people began to realize the sheer genius and masterpiece of a cartoon this is.