The dragons were genetically (or magically) engineered to be a slave race.
A rider can survive without his dragon, but when a rider dies, his dragon also dies. There is NO WAY something like this could have evolved naturally,note and aren't bonded dragons the result of an ancient elvish spell anyway? Also, the actual Hell, ancient elves? What kind of defect causes half of a partnership - that's supposed to be equal - to need the other, but not the other way around?- It's only said in the movie that dragons die when their Riders do. It's never explicitly said either way in the books, though it's implied that this isn't the case.
Brom can teleport.
How else was he able to get to Gil'ead from almost the Beor Mountains without Saphira, who was already in Gil'ead?
- Funnily enough, this would actually be plausible in the books: teleporting yourself is, per Word of God, possible but requires a gigantic store of energy, and Brom is carrying around a ring with just such a store, which he would only realistically use up in an emergency—such as saving Eragon's life.
