/ic/ - Artwork/Critique

Am I fucking retarded? I just don't understand the placement of her ribcage. Why does it look like her sternum is twisted the opposite way from the ribs? Ribcage is a solid bone, is it not? I understand that clavicles can move freely, but her sternum should be aligned with her ribs, right? Is it some perspective/fat/skin I am not getting? On the right I tried tracing the ribcage and on the left I drew what I assume the ribcage should look like with sternum tilted like this. I also tried pose like her in front of the mirror, but I am a fat fuck so it wasn't helpfull.