"The Heckling Hare" (lost original ending of Looney Tunes short; 1941)
The Heckling Hare is a 1941 Merrie Melodies cartoon, and the last to be directed by Tex Avery, however it originally had a different ending than the "safe landing" one you see on TV today.
The cartoon originally ended with Bugs and Willoughby, the dog in the short, plummeting endlessly from hole to hole, leaving Bugs and Willoughby's final fate left hanging.
It's not known what's the exact reason for Leon Schlesinger cutting this out, but a reason might be that risqué line, the fear of audiences thinking Bugs had died, or the sheer length of the fall sequence, Leon Schlesinger had the cartoon edited so that Bugs and Willoughby only fall off the cliff one time, rather than three. Then they safely land on the ground, feet-first. Bugs says, "Heh-heh. Fooled ya, hadn't we?". The cartoon ended there. The cut infuriated Avery, who promptly left to begin his historic run at Metro-Goldwyn Mayer, where he debuted his most famous character, Droopy.
No mention of the footage (which might have proven valuable for recycled use in other cartoons later on) being destroyed was ever made, but nor were any preservation efforts ever described, other than a transcript. The fate of film footage in that era, while better than prior ones, was still not at all a certain one. Fans of classic WB animation continue to search archives and collections for the possibility of finding this and other lost Bugs footage.