DL: Please tell me you were joking when you asked if it was her spine
It is her stomach but due to her lack of bodyfat she can suck in her sides. I have a friend who is even thinner than she is, it is awful to see her waste away like that :-S
You may optionally give an explanation for why this post was reported, which will be sent to the moderators along with the report. This can help the moderator to understand why you reported the post.