They are litter mates. It was just them two from birth as far as I know. I think the breeder didn't socialize with them... like ever, they were in the cage with their mother for the first month or so of their life. So it's possible Juliet just became introverted, while Isis is a tomboyish extrovert. She relies on her sister to lead the way, and avoids people, I'm the only one she comes to, in fact she's very attached to me, follows me everywhere, and sits by me (or on me) when I'm on the computer. She's very affectionate, but her affection is coupled with this almost masochistic fear. She's incredibly smart too, I've been playing fetch with her since she was 6 months old, and she always brings the ball right into my hands, or if I'm busy sets it down by my feet. I could go on for days about her. I love her just the way she is, and actually love the fact that they are so different, because I get the best of both worlds.