Ok, because this is part of Failed Experiments this might need some explanation. Katie and Cici used to be in a relationship, Katie took advantage of this and had Cici do everything for her, saying she was lucky to be with someone like her. One day they had an argument that went too far, Katie lost control of herself and cut off Cici's arm. She would have killed her if Cici hadn't run out of the house. She never got over the regret of doing this and has hidden her emotions, so she doesn't have to deal with it.