You may notice your bunny's butt twitching occasionally...especially when you are offering some particularly tasty treat, like a bit of banana (remember, not too much! Fat bunnies are cute, but they are NOT healthy.)
This is totally normal! We have no idea why on earth bunnies would evolve to twitch their rumps when eating something delicious, but it certainly is cute, and no cause for alarm!
Here's a particularly good video, with a particularly cute rump-related example: