Besides being full of sugar, I would think thatthey would stick to the rabbit's teeth. With critter kids inthe house, under foot all the time, I find that I don't dare letanything fall on the floor!!! There's always somebody makinga lunge for it if it does.
He will be alright, but it is definitely not something I would give to them on purpose, as they even upset a human's tummy. I must admit, mine got into a few twice by digging through things just to get to them. Bunnies can somehow smell them in the next room, and mine go CRAZY whenever I open a bag, so I stopped buying them, haha. Silly rabbits do not know how bad these things are for them
Welcome to RO! As others have said, a single gummy bear isn't cause for concern - your rabbit will be just fine! There's nothing inherently toxic in a gummy bear.
That said, rabbits ARE prone to diabetes if they get too much sugar or too many carbs in general from their diet (long-term). Gummy bears and most other carbs (including crackers, cereal, chips, pasta, etc.) should be avoided and things like fruit and non-leafy veggies (esp. carrots) should be fed in strict moderation according to HRS guidelines.
In other words, you shouldn't deliberately give sugary/starchy foods to your rabbit... but you don't need to freak out about a one-time snatch of something "forbidden".