In the second season, Aang learns Earthbending from Toph Beifong after he has a vision of the blind Earthbender in a swamp telling him to find her. On their journey, they are chased by Fire Princess Azula and her friends and Ty Lee. The group learns about the Day of Black Sun in a secret underground library, and they attempt to reveal the information to the Earth King at Ba Sing Se. However, their flying bison, Appa, is captured by Sandbenders. Aang grows upset and angry and confronts the Sandbenders, learning that Appa has been sold. After stopping a Fire Nation drill threatening the safety of Ba Sing Se, they look for Appa only to find themselves dealing with the Dai Li before exposing their leader's deception. The group reunites with Jet helping them find Appa at Dai Li headquarters. They expose the Hundred Year War to the Earth King, who promises to help them invade the Fire Nation. Soon after, Aang meets a guru who attempts to teach Aang to open his seven "chakras" in order to control the defensive 'Avatar State'; but when Aang perceives Katara in danger, he leaves before the seventh "chakra" is opened, and thus loses his progress until the seventh is opened. Though Aang manages to unlock the Seventh Chakra, he is fatally electrocuted by Azula. He is later brought back to life by Katara, using the spirit water given to her by the Northern Water Tribe at the start of the second season.