Elmer Fudd purchases a live rabbit, Bugs, from the store, with intent on making "wabbit stew". However, Bugs decides to take advantage of the setup and heckle Elmer by making him believe that he has "Rabbititis", a highly contagious dread disease with symptoms that include seeing spots before the eyes and assuming rabbit characteristics. Terrified out of his mind, Elmer tries to keep himself from catching Bugs' contamination as the rabbit spends the rest of the cartoon making him believe he has the "Rabbititis".
Hare Tonic provides examples of:
- Beardness Protection Program: Bugs' doctor disguise consists of a hat, sunglasses and a long, grey beard.
- Breaking the Fourth Wall: It starts with Bugs telling the audience that he can't just leave early. Then at the end, he convinces Elmer that the audience is infected with Rabbititis, causing Elmer to run away. And finally, Bugs reassures the audience that they haven't got Rabbititis only they appear to get it as he describes the symptoms to them.
- The Fourth Wall Will Not Protect You: The short ends with the implication that the entire audience just caught Rabbititis (although judging from Bugs' laugh at the fade out, it's clear that it's meant to be a put-on).
- Fully-Clothed Nudity: Elmer strips down to take a shower, but is still wearing his underwear.
- Mirror Routine: Bugs takes the mirror off the frame and pretends to be Elmer's reflection to make him think that he's turned into a rabbit.
- Saying Sound Effects Out Loud: Bugs when pretending to be Elmer's showerhead.Bugs: Gurgle, gurgle. Why don't you pay your water bill, Doc?
- Sequential Symptom Syndrome:
- As Bugs tells Elmer that he doesn't have the symptoms of Rabbititis, he manifests the symptoms as he mentions them.
- At the end, Bugs tells the audience that if they had Rabbititis, they'd see red and yellow spots before their eyes. As he says that, the screen is filled with red and yellow spots. Then Bugs says that the dots would start swirling around, and the dots do just that. Finally, he says that everything would go black and the screen fades to black, with Bugs snickering.
- Special Edition Title: This is one of two shorts ending with Bugs coming out of the Looney Tunes drum, chomping a carrot, and saying, "An' dat's de end." (The other being Baseball Bugs.)
- Squashed Flat: Elmer backs himself into a wall so hard he flattens out.
- Stewed Alive: Elmer puts a living Bugs in a pot on his stovetop.
- That Russian Squat Dance: Bugs tricks Elmer into doing it as he tests his reflexes. He then puts on a Cossack hat and boots and joins in. And he continues to dance even after Elmer realizes he's been tricked and gets his shotgun.
- Visual Pun: Bugs shows Elmer his coated tongue - that is, his tongue has a little overcoat on it.
- We Interrupt This Program: Bugs hides behind a radio and does a fake news bulletin about the spread of Rabbititis.
- You Don't Want to Catch This: Bugs invents the dread disease Rabbititis to mess with Elmer.
- Your Princess Is in Another Castle!: Bugs actually gets away early on, but then he realizes that "this set up is too good. I just can't leave. I gotta get back and heckle that character." So he comes back and does the whole Rabbititis routine.