A rabbit... There were some rabbit monsters back in Snowdin, but that's a surface rabbit! Uh, have you never seen a bunny before, or...?    

*Small anon gives Flowey a reassuring pet while the others shoo the bunny away.* Come on little buddy, it's gonna be alright... You okay, Flowey? No need to fear, it was just a bunny!

That would be a bunny, Flowey. Normally I'd say you'll be fine, but you're a plant. Flowey... bunnies, well... eat plants.