Bai Yun’s third cub, Su Lin, was born in 2005. Her name means “a little bit of something very cute,” and she was one of the smaller cubs. The panda keepers called her an “old soul,” saying that she was “mellow” and that sometimes she seemed more sensitive to environmental changes. Su Lin was the first cub trained to be part of the giant panda hearing study. Su Lin ended up staying at the Zoo until she was five years old, and during that time she went through her first estrus. Watching her scent mark her enclosure and even investigate her bedroom for possible denning was interesting for guests and staff.