It was during production of this cartoon that Bugs Bunny's name originated. Designer Charles Thorson redesigned the rabbit character and labeled the model sheet "Bug's Bunny," after co-director Ben Hardaway's nickname, Bugs.
The third of four apperances by the rabbit character who later evolved into Bugs Bunny. (The first was Porky's Hare Hunt (1938).)
Happy Rabbit's voice and laugh were identical to those of Woody Woodpecker in his very first appearance (the Andy Panda cartoon "Knock Knock", released the following year). In fact, Mel Blanc voiced Woody Woodpecker for the first year before entering a contract with Warner Bros.
There had been speculation about the real ending of this cartoon, as the version shown on television ends abruptly after the rabbits appear following the hunter threatening to beat up the wacky rabbit and his entire family. On April 27, 2009, animation historian David Gerstein posted a report on his blog that he finally revealed the true ending to this cartoon: the rabbits attack the hunter in a cartoon smoke cloud and then run away. The smoke clears up to show the hunter disheveled. The rabbit returns to give the hunter his busted rifle saying "You oughtta get that fixed. Somebody's liable to get hurt." He then returns to his looney self, bouncing on his head like a pogo stick down the road. The hunter becomes enraged, but then does the same thing the rabbit does. This scene might have been removed because, as Gerstein theorizes, the ending scene was similar to the ending of Tex Avery's "Daffy Duck & Egghead", which was released a year earlier prior to the release of "Hare-um Scare-um". The lost ending was restored on Looney Tunes Platinum Collection: Volume 2. Also, as of 2024, the full scene is included in Saturday morning showings on the MeTV network.
The goofy song that Happy Rabbit sings in this short would eight years later be modified and sung by Bugs Bunny in Easter Yeggs".