Meng Meng, who turned four in July, is deep into puberty. When she was first introduced to her garden habitat at the zoo in early July, she was as engaged and curious as any zoo’s CFO could hope, attracting visitors from across Europe. She climbed the trees, played on swings, splashed in the stream. But less than six months later, she began walking backwards. Her keepers have interpreted this behavior as the protest of a frustrated adolescent.