There are many things in the world that go unnoticed...and sometimes things that are noticed but completely misunderstood. For instance, I bet you probably don't remember SPECIFICALLY looking at a beautiful female model and noticing that she has a lot of definition in the area between the two tendons on either side of her throat (near the top of the ribcage). I mean, you notice the neck, but you don't really think about all the individual parts.

Aaaaaanyway, I was looking over some funny pictures and ran into a pic of a few women (topless) and realized why that's so common. They're sucking in their gut and that area also gets sucked in. Heh, that one woman (second from the left) is OBVIOUSLY sucking in her gut.