It's the sinew and the way your skin looks. You've always been slender, but this is something different. Perhaps it's the lighting and editing, but in this picture you do look like you're going to break any second. I find you and your photos stunning, but this one just makes me alarmed.
You probably take some of the most beautiful self-portraits I've ever seen. I remember being a younger photographer and always looking up to you and your photographs and wanting to be the same one day. I still look up to you- constantly and forever.