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A Costly Mistake is the 29th chapter of Eragon. It takes the point of view of Eragon.
Summary[]
Brom and Eragon leave Teirm. Eragon questions Brom about his past and the Varden, and learns that many of the conflicts between forces of Alagaësia are centered around him and the next generation of Riders. It is revealed that Brom killed Morzan fighting for Saphira's egg and that he wants to keep Eragon from the Varden as long as possible so that he will not get caught up in their politics.
Eragon breaks his wrist and they encounter Urgals. Eragon and Saphira reveal themselves and Eragon talks with them. They say that they serve a higher master. Eragon tries to lift and throw all twelve Urgals, but that proves to be beyond him and he passes out (again).