The twin female pandas, Mei Lun and Mei Huan, were born at Zoo Atlanta in 2013 but handed back to China this month under the rules of the "panda diplomacy" program under which China loans the endangered animals to other countries as a gesture of friendship.
The twins' parents, Lun Lun and Yang Yang, have been on loan to Zoo Atlanta since 1999, and Mei Lun and Mei Huan were the first twin pandas born in the U.S. to survive.
But Chinese media reported this week that the twin sisters were having problems adjusting to their new home at the Chengdu Research Base of Giant Panda Breeding, where they have been since November 5.
"The naughty twins refused to eat traditional Chinese food like steamed bread of corn, and preferred American biscuits instead," Xinhua elaborated.
Mei Lun and Mei Huan also do not understand the local Chinese dialect and only respond to basic commands in English, the Communist Party-run People's Daily reported.
Researchers were trying to wean them off cookies, the newspaper added.